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问题 单项选择题

导致人体摄取氟过多的氟来源中，可能性最小的是

A．食品氟

B．饮水氟

C．含氟牙膏

D．空气氟

E．含氟涂膜

答案

参考答案：E

解析：除本选项外，其余途径均存在过量摄入氟的危险。

选择题

实验室为除去苯中含有的少量苯酚，通常采用的方法是 [ ]

A．加热蒸馏，用分馏法分离

B．加乙醇，用分液漏斗分离

C．加氢氧化钠溶液，用分液漏斗分离

D．加浓溴水，用过滤法分离

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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 (53) of fifteen hours a week on a daytime 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 European 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.

51().

A. establish

B. purchase

C. prove

D. attend
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