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Internet History
因特网史
Expanding on the freeway metaphor, with cars, there are various levels of knowledge; learning to drive is easy, and it is all you really need to know about cars. This is like learning to surf the Internet. In the course of driving, you learn about highways, shortcuts, and so on, and using the Web is very similar, that is, with practice, you will learn where and how to find things.
Also, in driving, you can go another step and learn how an engine works and how to do routine maintenance and repairs, such as oil changes and tune-ups. On the Web, the equivalent is to learn how Web pages are put together, which you have already started to do.
A still deeper level of involvement with cars is learning how to do complex repairs, or to design and build them. Not many people pursue cars to this stage. On the Web, a similar level of involvement is writing software, either building applets[1]in a language such as Java[2], or developing more general-purpose tools for others to use in navigating the Web. Again, only a limited number of people aspire to this level.
Today, the Information Superhighway is in place, but for many people, the mysteries surrounding it involve where to go and how to travel. Like traveling a highway in a foreign country and being unable to read the road signs, navigating the Information Superhighway can be frustrating and time-consuming without the right knowledge and tools.
Consider that there are many ways to travel sidewalks, roads, and freeways to get to where we want to go. We can take a bicycle, a bus, a car, or a pair of in-line skates. Similarly, there are many ways to use the Internet to send and retrieve information. These include, but are not limited to[3]: e-mail, file transfer, remote login, and the Web. New methods of using the Internet will probably be conceived and developed in the near future, and existing methods will be improved.
Internet History
The history of the Internet is best explained via a timeline. We have included events that were important and required innovation, as well as other interesting and related items. For each item mentioned on the timeline, we provide a brief synopsis. While the timeline begins in 1969, we present some general comments on the 1960s, for background. The history of the Internet is fascinating both for itself and as a case study of technological innovation.
Essential to the early Internet concept was packet switching[4], in which data to be transmitted was divided into small packets of information and labeled to identify the sender and recipient. The packets were sent over a network and then reassembled at their destination. If any packet did not arrive or was not intact, the original sender was requested to resend the packet. Prior to packet switching, the less efficient circuit switching method of data transmission was used. In the early 1960s, several papers on packet switching theory were written, laying the groundwork for computer networking as it exists today.
In 1969, Bolt, Beranek, and Newman, Inc., (BBN)[5]designed a network called the Advanced Research Projects Agency Network (ARPANET)[6]for the United Sates Department of Defense. The military created ARPANET to enable researchers to share "super-computing" power. It was rumored that the military developed the ARPANET in response to the threat of a nuclear attack destroying the country's communication system.
Initially, only four nodes (or hosts) comprised the ARPANET. They were located at the University of California at Los Angeles, the University of California at Santa Barbara, the University of Utah, and the Stanford Research Institute. The ARPANET later became known as the Internet.
In the 1970s, the ARPANET was used primarily by the military, some of the larger companies, such as IBM, and universities (for e-mail). The general population was not yet connected to the system and very few people were on-line at work.
The use of local area networks (LANs) became more prevalent during the 1970s. Also, the idea of an open architecture was promoted; that is, networks making up the ARPANET could have any design. In later years, this concept had a tremendous impact on the growth of the ARPANET.
By 1972, the ARPANET was international, with nodes in Europe at the University College in London, England, and the Royal Radar Establishment in Norway. The number of nodes on the network was up to 23, and the trend would be for that number to double every year from then on. Ray Tomlinson, who worked at BBN, invented e-mail.
In 1979 user Network (USENET) was started by using UUCP[7]to connect Duke University and the University of North Carolina at Chapel Hill. Newsgroups emerged from this early development.
In the 1980s, Transmission Control Protocol/lnternet Protocol (TCP/IP)[8], a set of rules governing how networks making up the ARPANET communicate, was established. For the first time, the term "Internet" was being used to describe the ARPANET. Security became a concern, as viruses appeared and electronic break-ins occurred.
The 1980s saw the Internet grow beyond being predominantly research oriented to including business applications and supporting a wide range of users. As the Internet became larger, the Domain Name System (DNS) was developed, to allow the network to expand more easily by assigning names to host computers in a distributed fashion.
The Computer Science Network (CSNET) connected all university computer science departments in the United States. Computer science departments were relatively new, and only a limited number existed in 1980. CSNET joined the ARPANET in 1981. Two years later the United States Defense Communications Agency required that TCP/IP be used for all ARPANET hosts. Since TCP/IP was distributed at no charge, the Internet became what is called an open system. This allowed the Internet to grow quickly, as all connected computers were now "speaking the same language. " Central administration was no longer necessary to run the network.
In 1985, the National Science Foundation Network (NSFNET)[9]was formed to connect the National Science Foundation's (NSF's) five super-computing centers. This allowed researchers to access the most powerful computers in the world, at a time when large, powerful, and expensive computers were a rarity and generally inaccessible.
The virus called Internet Worm[10](created by Robert Morris while he was a computer science graduate student at Cornell University) was released. It infected 10 percent of all Internet hosts. Also in this year, Internet Relay Chat(IRC)[11]was written by Jarkko Oikarinen.
NSF took over control of the ARPANET in 1989. This changeover went unnoticed by nearly all users. Also, the number of hosts on the Internet exceeded the 100,000 mark.
During the 1990s, lots of commercial organizations started getting on-line. This stimulated the growth of the Internet like never before. URLs[12]appeared on television advertisements and, for the first time, young children went on-line in significant numbers.
Graphical browsing tools were developed, and the programming language HTML[13]allowed users all over the world to publish on what was called the World Wide Web. Millions of people went on-line to work, shop, bank, and be entertained. The Internet played a much more significant role in society, as many non-technical users from all walks of life got involved with computers. Computer-literacy and Internet courses sprang up all over the country.
Gopher[14]was developed at the University of Minnesota, whose sports team's mascot is the Golden Gopher. Gopher allowed you to "go for" or fetch files on the Internet using a menu based system. Many gophers sprang up all over the country, and all types of information could be located on gopher servers. Gopher is still available and accessible through Web browsers, but its popularity has faded; for the most part, it is only of historical interest.
In 1991, the World Wide Web (WWW) was created as a simple way to publish information and make it available on the Internet. The interesting nature of the Web caused it to spread, and it became available to the public in 1992. Those who first used the system were immediately impressed.
Mosaic[15], a graphical browser for the Web, was released by Marc Andreessen and several other graduate students at the University of Illinois, the location of one of NSF's super-computing centers. Sometimes you will see Mosaic referred to as NCSA[16]Mosaic, where NCSA stands for the National Center for Supercomputing Applications. Mosaic was first released under X Windows and graphical UNIX[17]. To paraphrase a common idiom, each person who used the system loved it and "told five friends," and Mosaic's use spread rapidly.
The company called Netscape Communication, formed by Marc Andreessen and Jim Clark, released in 1994 Netscape Navigator, a Web browser that captured the imagination of everyone who used it. The number of users of this software grew at a phenomenal rate. Netseape made (and still makes) its money largely through advertising on its Web pages. And in the same year, Stanford graduate students David Filo and Jerry Yang developed their Internet search engine and directory called Yahoo, which is now world-famous. One year later, the Internet programming environment, Java, was released by Sun Microsystems, Inc. This language, originally called Oak, allowed programmers to develop Web pages that were more interactive.
The software giant, Microsoft, in 1995, committed many of its resources to developing its browser, Microsoft Internet Explorer, and Internet applications. Some of the first courses about the Internet were given in the meanwhile. Course development has been difficult, because of the rapidly changing software. In 1998, Netscape Communications released the source code for its Web browser.
Notes
[1] applets: 应用程序片段，小应用程序，用Java语言编写的一种应用程序。
[2] Java: Java语言。美国Sun公司的James Gosling于1990年编制的一种计算机语言，1995年首次公布，Java是在C++语言基础上发展起来，语法上与C++相似的一种面向对象的语言。
[3] These include, but are not limited to: 这些包括，但不限于……
[4] packet switching：(数据、信息)包交换法，(报文)分组交换技术(借助编址的报文分组选择路由并发送数据，以使一个信道只在包传送时才被占用的处理方法或技术)。
[5] Bolt, Beranek, and Newman, Inc.，(BBN)：BBN公司，美国马萨诸塞州的一个公司，早期维护ARPANET网，后来维护因特网的核心网关。
[6] the Advanced Research Projects Agency Network (ARPANET)：阿帕网，ARPA网(高级研究计划局的计算机网络名)。
[7] UUCP: Unix到Unix的拷贝程序(UNIX to UNIX Copy)。UUCP是Usenet用于数据传输的主要通讯协议之一。
[8] Transmission Control Protocol/lnternet Protocol (TCP/IP)：传输控制协议/网络协议。
[9] the National Science Foundation Network (NSFNET)：自然科学基金网。
[10] Internet Worm：因特网虫(1988年美国康奈尔大学的一个学生写的字符串自复制开玩笑程序，一夜之间遍布整个因特网，导致大多数计算机停止运行)。
[11] Internet Relay Chat(IRC)：因特网交谈服务系统(使用文本实时交谈，可多人参加)。
[12] URLs (Uniform Resource Locator)：统一资源地址、统一资源定位器(程序)。
[13] HTML(Hypertext Markup Language)：超文本链接标示语言。
[14] Gopher：跑腿鼹鼠，是用户在因特网上的个人图书管理员，供用户查询搜索所需的系统资源。
[15] Mosaic：1993年因特网上出现的第一个图形界面Web浏览器。
[16] NCSA (National Center for Supercomputing Application)：国家超级计算应用中心。
[17] Unix: 一种多用户的计算机操作系统。
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Computer and Its Kind
计算机及其种类
A computer is an electronic device that can receive a set of instructions, or program, and then carry out this program by performing calculations on numerical data or by compiling and correlating other forms of information.
The modern world of high technology could not have come about except for the development of the computer. Different types and sizes of computers find uses throughout society in the storage and handling of data, from secret governmental files to banking transactions to private household accounts[1]. Computers have opened up a new era in manufacturing through the techniques of automation, and they have enhanced modern communication systems. They are essential tools in almost every field of research and applied technology, from constructing models of the universe to producing tomorrow's weather reports, and their use has in itself opened up new areas of conjecture. Database services and computer networks make available a great variety of information sources[2]. The same advanced techniques also make the invasions of privacy and restricted information sources possible, and computer crime has become one of the many risks that society must face if it is to enjoy the benefits of modern technology.
Types of Computers
1. Microcomputer
A microcomputer is a desktop or notebook size computing device that uses a microprocessor as its Central Processing Unit, or CPU. Microcomputers are also called Personal Computers (PCs) , home computers, small business computers, and micros. The smallest, most compact are called laptops. When they first appeared, they were considered single user devices, and they were capable of handling only 4, 8, or 16 bits of information at one time. More recently the distinction between microcomputers and large, mainframe computers as well as the smaller mainframe type systems called minicomputers has become blurred, as newer microcomputer models have increased the speed and data handling capabilities of their CPUs into the 256 bit, or even much more bit multiuser range.
Microcomputers are designed for use in homes, schools, and office settings. Within the home, they can serve both as a tool for home management balancing the family checkbook, structuring the family budget, indexing recipes and as a recreational device playing computer games, cataloging records and books. School children can use microcomputers for doing their homework, and in fact many public schools now employ the devices for programmed learning and computer literacy[3]courses. Small businesses may purchase microcomputers for word processing, bookkeeping, the storage and handling of mailing lists and so on.
Desktop Computer
A desktop computer is a personal computer in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Prior to the wide spread of microprocessors a computer that could fit on a desk was considered remarkably small. Today the phrase usually indicates a particular style of computer case. Desktop computers come in a variety of styles ranging from large vertical tower cases to small form factor models that can be tucked behind an LCD[4]monitor. In this sense the term "desktop" refers specifically to a horizontally-oriented case, usually intended to have the display screen placed on top to save space on the desk top. Most modern desktop computers have separate screens and keyboards. A specialized form of desktop case is used for home theater PC systems, incorporating front-panel mounted controls for audio and video.
Personal Digital Assistant (PDA)[5]
A personal digital assistant (PDA) is a handheld computer, also known as a palmtop computer. Newer PDAs also have both color screens and audio capabilities, enabling them to be used as mobile phones, smartphones, web browsers, or portable media players. Many PDAs can access the Internet, intranets or extranets via Wi-Fi[6], or Wireless Wide-Area Networks (WWANs[7]). Many PDAs employ touch screen technology.
Tabjet[8]PC
A Tablet PC is a laptop mobile computer, equipped with a touchscreen or graphics tablet/screen hybrid technology which allows the user to operate the computer with a stylus or digital pen, or a fingertip, instead of a keyboard or mouse. This form factor offers a more mobile way to interact with a computer. Tablet PCs are often used where normal notebooks are impractical or unwieldy, or do not provide the needed functionality.
Laptop[9]
A laptop (also known as a notebook) is a personal computer designed for mobile use small enough to sit on one's lap. A laptop includes most of the typical components of a typical desktop computer, including a display, a keyboard, a pointing device, a touchpad, also known as a trackpad, or a pointing stick, as well as a battery, into a single small and light unit. The rechargeable battery required is charged from an AC/DC adapter and typically stores enough energy to run the laptop for several hours.
2. Minicomputer
A minicomputer is a mid-level computer built to perform complex computations while dealing efficiently with a high level of input and output from users connected via terminals. Minicomputers also frequently connect to other minicomputers on a network and distribute processing among all the attached machines. Minicomputers are used heavily in transaction processing applications and as interfaces between mainframe computer systems and wide area networks.
3. Mainframe Computer
A mainframe computer is a high level computer designed for the most intensive computational tasks. Mainframe computers are often shared by multiple users connected to the computer via terminals. The most powerful mainframes, called supercomputers, perform highly complex and time-consuming computations and are used heavily in both pure and applied research by scientists, large businesses, and the military.
4. Others
·Servers
A server usually refers to a computer that is dedicated to providing a service. For example, a computer dedicated to a database may be called a "database server". "File servers" manage a large collection of computer files. "Web servers" process web pages and web applications. Many smaller servers are actually personal computers that have been dedicated to providing services for other computers.
A server is a computer program that provides services to other computer programs and their users in the same or other computer. The physical computer that runs a server program is also often referred to as server.
Services can be supplied centrally by the use of a server; in other cases all the machines on a network have the same status with no dedicated server, and services are supplied peer-to-peer[10].
·Workstation
Workstations are computers that are intended to serve one user and may contain special hardware enhancements not found on a personal computer.
It is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems. The term workstation has also been used to refer to a mainframe computer terminal or a PC connected up to a network.
Historically, workstations had offered higher performance than personal computers, especially with respect to graphics and CPU power, memory capacity and multitasking ability. They are optimized for display and manipulation of different types of complex data such as?3D mechanical design,?engineering simulation (e. g. computational fluid dynamics), animation and rendering of images, and mathematical plots. Consoles consist of a high resolution display, a keyboard and a mouse at a minimum, but also offer multiple displays, graphics tablets, SpaceBalls, etc. Workstations are the first segment of the computer market to present advanced accessories and collaboration tools.
·Embedded computers
Embedded computers are computers that are a part of a machine or device. Embedded computers generally execute a program that is stored in non-volatile memory and is only intended to operate a specific machine or device. Embedded computers are very common. Embedded computers are typically required to operate continuously without being reset or rebooted, and once employed in their task the software usually cannot be modified. An automobile may contain a number of embedded computers; however, a washing machine and a DVD player would contain only one. The central processing units (CPUs) used in embedded computers are often sufficient only for the computational requirements of the specific application and may be slower and less expensive than CPUs found in personal computers.
·Supercomputer
In computer science, supercomputers are large, extremely fast, and expensive computers used for complex or sophisticated calculations, typically, machines capable of pipelining instruction execution and providing vector instructions. A supercomputer can, for example, perform the enormous number of calculations required to draw and animate a moving spaceship in a motion picture[11]. Supercomputers are also used for weather forecasting, large scale scientific modeling, oil exploration and so on and so like.
Future Developments
One ongoing trend in computer development is microminiaturization, the effort to compress more circuit elements into smaller and smaller chip space. Researchers are also trying to speed up circuitry functions through the use of superconductivity, the phenomenon of decreased electrical resistance observed as objects exposed to very low temperatures become increasingly colder[12]. The fifth-generation computer, the effort to develop computers that can solve complex problems in what might eventually be called creative ways, is another trend in computer development, the ideal goal being true artificial intelligence[13].
Quantum Computer
A quantum computer[14], quite different from classical current computers, is a device that harnesses physical phenomenon unique to quantum mechanics to realize a fundamentally new mode of information processing. In a quantum computer, the fundamental unit of information called a quantum bit (or qubit), is not binary but rather more quaternary in nature.?A qubit can exist not only in a state corresponding to the logical state 0 or 1 as in a classical bit, but also in states corresponding to a blend or superposition of these classical states. In other words, a qubit can exist as a 0, a 1, or simultaneously as both 0 and 1, with a numerical coefficient representing the probability for each state.
DNA Computer
DNA computing[15]is a form of computing which uses DNA, biochemistry and molecular biology, instead of the traditional silicon-based computer technologies. DNA computing, or. more generally, molecular computing, is a fast developing interdisciplinary area and is fundamentally similar to parallel computing in that it takes advantage of the many different molecules of DNA to try many different possibilities at once. And DNA computers are faster and smaller than any other computer built so far.
Optical Computer[16]
An optical computer is a computer that uses light instead of electricity (i. e.photonsrather thanelectrons) to manipulate, store and transmit data. Optical computer technology is still in the early stages: functional optical computers have been built in the laboratory, but none have progressed past the prototype stage.
Molecule Computer
A molecular computer that uses enzymes to perform calculations has been built and it is believed enzyme-powered computers could eventually be implanted into the human body and used to, for example, tailor the release of drugs to a specific person's metabolism.
It used two enzymes to trigger two interconnected chemical reactions. Two chemical components-hydrogen peroxide[17]and glucose[18]-were used to represent input values A and B. The presence of each chemical corresponded to a binary 1, while the absence represented a binary 0. The chemical result of the enzyme-powered reaction was determined optically.
Notes
[1]... from secret governmental files to banking transactions to private household accounts.
①from... to:从……到。
②banking transactions to：对……的金融交易此处指银行转账，大意为：从政府的秘密文件到银行对私人家庭账户的账目往来。
[2]... make available a great variety of information sources. 本句和下一句均为倒装句，在宾语过长而其补语太短的情况下，常使用这一结构。原结构应为“to make sth. available/possible”。
[3]computer literacy计算机扫盲。“literacy”，原意为“识字，扫盲，有读和写的能力”，这里引申为“使用计算机的基本能力”。
[4]LCD (liquid crystal display)液晶显示，通过将具有极性分子结构的液体混合物夹在两个透明的电极间构成的显示方式。
[5]Personal Digital Assistant (PDA)个人数字助理。它是一种轻便的掌上型计算机，既有通信功能，又有个人组织功能，包括日历、笔记、数据库、计算器等。
[6]Wi-Fi (Wireless Fidelity)无线保真，是一种可以将个人电脑、手持设备，如PDA、手机等终端以无线方式互相连接的技术。Wi-Fi一词由Wi-Fi产业联盟(Wi-Fi Alliance)提出。
[7] WWAN (Wireless Wide-Area Networks)无线广域网，WWAN技术是使得笔记本电脑或者其他的设备装置在蜂窝网络覆盖范围内可以在任何地方连接到互联网，其下载速度可以与DSL相媲美。
[8]tablet图形输入板，在工程、设计和解释类的应用程序中用于输入图形位置信息的设备。
[9]laptop便携式计算机，一种为便于旅行时使用而设计的小型手提式计算机，可用电池或交流电源供电。
[10]peer-to-peer (P2P.)点对点技术，又称对等互联网络技术，是一种网络新技术，依赖网络中参与者的计算能力和带宽，而不是把依赖都聚集在较少的几台服务器上。P2P网络通常用于通过Ad Hoc连接来连接节点，也被使用在类似VoIP等实时媒体业务的数据通信中。纯点对点网络没有客户端或服务器的概念，只有平等的同级节点，同时对网络上的其他节点充当客户端和服务器。也有些专家称P2P是点对点技术，但其实是错的，实应解作群对群(Peer-to-Peer)。在虚拟私人网络VPN(Virtual Private Network)中，也有P2P这个名称，它才应解作点对点(Point-to-Point)。
[11]motion picture电影。
[12]..., the phenomenon of decreased electrical resistance observed as objects exposed to very low temperatures become increasingly colder. 此处，过去分词“observed”用作定语，修饰名词“the phenomenon”，它所带的状语从句中的过去分词短语“exposed to”修饰名词“objects”。可以翻译成“当暴露于超低温的物体的温度越来越低时，即可观察到电阻值降低的现象”。
[13]...，the ideal goal being true artificial intelligence. 分词独立结构，句中起说明作用，可翻译成“理想的目标是真正的人工智能”。
[14]quantum computer量子计算机，由理查德·费曼提出，是从物理现象的模拟而来的。量子电脑能做出对数运算，而且速度远胜传统电脑。这是因为量子不像半导体只能记录0与1，可以同时表示多种状态，一个40位元的量子电脑，就能解开1024位元电脑花上数十年解决的问题。
[15]DNA computing，DNA运算，或译DNA计算，是一种电脑运算形式，利用DNA、生物化学以及分子生物学原理，而非传统上以硅为基础的电脑技术。
[16]optical computer光学计算机，利用可见光或红外光而不是电流进行数据处理，从全息存储、激光存储或存储库输入数据的计算器，多用于指纹鉴定和图像清晰化的处理过程。
[17]hydrogen peroxide过氧化氢：一种无色、重、具有很强氧化作用的液体H2O2。
[18]glucose葡萄糖：一种单糖，C6H12O6，广见于大多数动植物组织。
第5题
回忆间的乳娘，情人中的情人，
你啊，我的欢娱，你啊，我的苦差!
有朝一日你会记得爱的抚摸，
记得内室的静和黄昏的绮丽。
回忆间的乳娘，情人中的情人。
黄昏给大城的煤火照得通红；
在凉台上，沉浸玫瑰色烟雾中
你的胸脯是多么温，心灵多么柔，
我们曾低诉那样隽永的话语。
黄昏给大城的煤火照得通红。
炽热黯光里的夕阳绚烂无比；
空间无比深沉，心灵无比健壮，
俯身向你，你，令我心倾的天仙，
我自觉闻嗅到你赤血的芳香，
炽热黯光里的夕阳绚烂无比。
夜色逐渐变浓． 凝成一道厚墙，
黯里我的眼光寻索着你的双眸，
渴饮你的气息，啊，甘露，啊，毒汁!
你的脚倦憩在我紧握的手里，
夜色逐渐变浓，凝成一道厚墙。
我有追叙那欢乐时刻的才能，
我的过去卷伏在你的双膝前。
无需到他处去寻觅你的美质，
它在你的肉体上，也在你的柔情里!
我有追叙那欢乐时刻的才能。
啊，誓言，啊，芳香，啊，无尽的热吻!
它们将无底的深渊中再生么？
宛若那些在大海底浸浴过的
回春之阳，它们再度飞升晴空……
啊，誓言，啊，芳香，啊，无尽的热吻!
第6题
A．有差异，能区别词义??B．有差异，但不能区别词义
C．没有差异，不能区别词义??D．没有差异，但能区别词义
第9题
A．顋(sī)；一晌(shǎnɡ)；撚(niǎn)；醽醁(línɡlù)
B．瀰(mǐ)瀰；敧枕(qīzhèn)；瘗(yì)；亸(dān)凤
C．纶(ɡuān)巾；鸣蛩(qiónɡ)；钏(chuàn)；迍(zhūn)迍；
D．花簟(diàn)；猊(ní)；宝匳(lián)；谂(niǎn)知
第10题
(1)在那些艰难的日子里，不管他的身体有多差，生活条件再不好，精神压力有多大，他都坚持创作。
(2)尽管国外给了他怎样优厚的条件，他还是坚决地回到了祖国的怀抱。
(3)我们因为刚栽下的树苗能够成活，头顶烈日给它们浇水。
(4)为了他又同意了，所以会议如期举行。
(5)如果了解了同学们的想法，组织了丰富多彩的活动，加强了团结，我们班才能取得这样大的进步。
(6)他没受到多少教育，也不擅言辞，所以很能干，还不时得到大家的好评。
(7)“文化大革命”期间，他很年轻，曾干过不少傻事，但在那样的环境下，多少年轻人的青春就断送在所干的这些傻事里!
(8)这部作品虽然写的是农民，却也深刻地表现了广大农民的愿望。
(9)如果干什么事，只有掌握了科学的方法，才可以收到事倍功半的效果。
(10)人们只有解放思想，努力学习，就可以掌握科学技术知识，并且有可能成为科学家。
第11题
A．[i]和[y]的区别是舌位前后不同
B．[u]和[o]的区别是舌位高低不同
C．[a]和ɑ的区别是舌位前后不同
D．[i]和[a]的区别是舌位高低不同
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