回声echo

●向目标发送ICMP回声请求(echo)报文的命令是 (46) 。

(46) A. Tracert

B.Arp

C.Nslookup

D. Netstat

●向目标发送ICMP回声请求(echo)报文的命令是 (46) 。

(46) A. Tracert

B.Arp

C.Nslookup

D. Netstat

A、报告错误

B、检查节点（node）之间的通达性

C、检查IP分组的生存时间

D、发现IP地址

dinary discovery of echolocation (回声定位) in bats to see a case in which the voice plays a strictly practical role.

To get a full appreciation of what this means we must turn first to some recent human inventions. Everyoneknows that if he shouts near a wall or a mountainside, an echo will come back. The further off this solid obstacle, the longer time it will take for the return of the echo. A sound made by tapping on the main body of a ship will be reflected from the sea bottom, and by measuring the time interval between the taps andthe receipt of the echoes the depth of the sea at that point can be calculated.So was born the echo-sounding equipment, now in general use in ships. Every solid object will reflect a sound, varying according to the size and nature of the object. A shoal of fish will do this. So it is a comparatively simple step fromlocating the sea bottom to locating a shoal of fish. With experience, and with improved equipment, it is now possible not only to locate fish but to tell if it is herring, cod, or other well-known fish, by the pattern of its echo.

A few years ago it was found that certain bats emit squeaks (吱吱声) and by receiving ’he echoes they could locate and steer clear of obstacles--or locate flying insects on which they feed.This echolocation in bats is often compared with radar, the principle of which is similar.@@@@@@@ Choose correct answers to the question:

The main purpose of this passage is to ______.

A.describe that animals can make different sounds

B.prove that animals’ voices can play practical roles

C.inspire the readers to make more inventions

D.startle the readers with some shocking facts

The discovery of echolocation may help with all of the following EXCEPTA.measuring the depth of the sea

B.distinguishing different kinds of fish

C.improving the functions of radar

D.varying the size and nature of an object

By saying "A shoal of fish will do this"(Lines 6-7, Para 2), the author means ________.A.only one special kind of fish can reflect sounds

B.only one special kind of fish can be used to help locate a ship

C.a large group of fish can reflect sounds

D.a large group of fish can be used to help locate a ship

As it is discussed in the passage, the squeaks of bats can be functionally compared with ________.A.human languages

B.a mountainside

C.a shoal of fish

D.taps on a ship

Which of the following statements can be inferred from the passage？A.Animals are more intelligent than humans.

B.Humans are more intelligent than animals.

C.Animals are often compared with human inventions.

D.Humans are often inspired by animals.

A、源抑制（source-quench）

B、目标不可达（destination-unreachable）

C、回声请求（echo-request）

D、重定向（redirectiong）

Not all sounds made by animals serve as language, and we have only to turn to that extraordinary discovery of echolocation (回声定位) in bats to see a case in which the voice plays a strictly practical role.

To get a full appreciation of what this means we must turn first to some recent human inventions. Everyoneknows that if he shouts near a wall or a mountainside, an echo will come back. The further off this solid obstacle, the longer time it will take for the return of the echo. A sound made by tapping on the main body of a ship will be reflected from the sea bottom, and by measuring the time interval between the taps andthe receipt of the echoes the depth of the sea at that point can be calculated.So was born the echo-sounding equipment, now in general use in ships. Every solid object will reflect a sound, varying according to the size and nature of the object. A shoal of fish will do this. So it is a comparatively simple step fromlocating the sea bottom to locating a shoal of fish. With experience, and with improved equipment, it is now possible not only to locate fish but to tell if it is herring, cod, or other well-known fish, by the pattern of its echo.

A few years ago it was found that certain bats emit squeaks (吱吱声) and by receiving ’he echoes they could locate and steer clear of obstacles--or locate flying insects on which they feed.This echolocation in bats is often compared with radar, the principle of which is similar.@@@@@@@ Choose correct answers to the question:

The main purpose of this passage is to ______.

A.describe that animals can make different sounds

B.prove that animals’ voices can play practical roles

C.inspire the readers to make more inventions

D.startle the readers with some shocking facts

The discovery of echolocation may help with all of the following EXCEPTA.measuring the depth of the sea

B.distinguishing different kinds of fish

C.improving the functions of radar

D.varying the size and nature of an object

By saying "A shoal of fish will do this"(Lines 6-7, Para 2), the author means ________.A.only one special kind of fish can reflect sounds

B.only one special kind of fish can be used to help locate a ship

C.a large group of fish can reflect sounds

D.a large group of fish can be used to help locate a ship

As it is discussed in the passage, the squeaks of bats can be functionally compared with ________.A.human languages

B.a mountainside

C.a shoal of fish

D.taps on a ship

Which of the following statements can be inferred from the passage?A.Animals are more intelligent than humans.

B.Humans are more intelligent than animals.

C.Animals are often compared with human inventions.

D.Humans are often inspired by animals.

请帮忙给出每个问题的正确答案和分析，谢谢！