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问题 选择题

常温时，将的醋酸滴加到的烧碱溶液中，下列结论正确的是

A．若混合溶液的，则混合溶液中

B．若混合溶液的，则混合溶液中

C．若，且混合溶液，则必有

D．若，，则混合溶液中

答案

答案：D

根据电荷守恒c(H＋)＋c(Na＋)=c(CH3COO－)+c(OH－)可知，如果pH大于7，则c(Na＋)大于c(CH3COO－)，A不正确。如果pH＝7，则c(Na＋)=c(CH3COO－)，B不正确。PH小于7，说明溶液显酸性，此时醋酸一定是过量的，所以c1大于c2，C不正确。选项D中二者恰好反应，生成的醋酸钠水解显碱性，根据质子守恒可知，D正确，答案选D。

判断题

发现混频晶体连续烧坏，首先应检查收发开关。
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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 (51) an educational institution, and they are required to study for a minimum of fifteen hours a week on a (52) course. Prospective students have to show that they can afford their studies, and that they have sufficient (53) resources to support themselves (54) in this country.

In order to work here the foreigner needs a work permit, (55) must be applied for by his prospective employer. The problem here is that the Department of Employment has the right to grant or (56) these permits, and there is little that can be done (57) it; it would be extremely unwise for a foreign visitor to work (58) 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 (59) 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 (60) part-time jobs while they are studying here.

54().

A.after 

B.but 

C.while 

D.before
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