SECTION B PASSAGES
Directions: In this section, you will hear several passages. Listen to the passages carefully and then answer the questions that follow.
听力原文: Canals are watercourses constructed to improve and extend natural waterways. (11) They are generally built to facilitate transportation, but from the beginning they have been used for many additional purposes including draining swamps, irrigating land for cultivation, and promoting economic development.
(11) Canals are often classified by the size of vessel they can accommodate. Some small local canals, which are able to float only 100 to 300 ton boats or small rafts of timber, may be only 3 feet deep. Major barge canals generally range from 6 to 9 feet in depth, and some are as much as 10 or 12 feet deep. These canals can carry 1,350 to 2,000 ton craft. Ship canals are 25 feet or more deep and are capable of accommodating large vessels in the seagoing class.
Canals may also be classified as either water level or lock canals. (13) Water level canals do not vary in height along their courses. The best known of these is the Suez Canal, which is at sea level, Lock canals, which include most modern waterways, contain locks, or special devices for raising and lowering boats along their courses by changing the depth of the water. (12) Each lock is a stretch of water enclosed by gates at each end. After a boat enters the lock, water is let or drained out until it reaches approximately the same level as the water ahead.
What does the passage mainly discuss?
A.How canals are constructed.
B.Common types of canal boats and barges.
C.The world's largest canals.
D.How canals are used and classified.
第1题
阿尔茨海默病的主要病理特征是
A.脊髓后索变性
B.小脑皮质脱髓鞘
C.大脑皮质神经元丢失
D.海马色素变性
E.小脑皮质神经元丢失
第6题
下述根据病理损害的范围及临床特征对脑变性疾病的分类中不正确的是()。
A、脊髓变性,包括进行性痉挛截瘫、进行性后索变性等;自主神经系统变性
B、大脑皮质变性,包括阿尔茨海默病、额颞叶痴呆
C、脑干小脑变性,包括小脑共济失调、脊髓小脑变性、橄榄-脑桥-小脑变性等
D、基底节变性,包括帕金森病、纹状体-黑质变性等;运动系统变性病,包括各种运动神经元病
E、黑质多巴胺能神经元变性缺失,路易小体形成
第10题
阿尔茨海默病的病理特征以下哪种说法是不正确的
A.大脑皮质弥漫性萎缩
B.脑沟增宽
C.老年斑和神经元纤维缠结
D.脑室扩大
E.神经元气球样肿胀
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