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问题 单项选择题

钢管水浸法聚焦法探伤时，下面有关线聚焦方式的叙述中，哪条是正确的？（）

A.探伤速度较快

B.回波幅度随缺陷长度增大而增高

C.聚焦方法一般采用圆柱面透镜或瓦片型镜片

D.以上全部

答案

参考答案：D

单项选择题

Visitors to this country are normally admitted for six months, but foreign students can usually stay for one year. They must (52) an educational institution, and they are required to study for a minimum of fifteen hours a week on a (53) course. Prospective students have to show that they can afford their studies, and that they have sufficient (54) resources to support themselves (55) in this country.

In order to work here the foreigner needs a work permit, (56) must be applied for by his prospective employer. The problem here is that the Department of Employment has the right to grant or (57) these permits, and there is little that can be done (58) it; it would be extremely unwise for a foreign visitor to work (59) a permit, since anyone doing so is liable to immediate deportation (驱逐出境). There are some people from the Common Market countries, who are often given (60) residence permits of up to five years. Some other people, such as doctors, foreign journalists, authors and others can work without permits, and foreign students are normally allowed to (61) part-time jobs while they are studying here.

55().

A.after 

B.but 

C.while 

D.before
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问答题 简答题

实现输煤系统程控对机械设备有何要求？
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