1. Suppose there were a flood or an earthquake and the people could not be reached by trains or trucks. _______ packages of food could be dropped from planes, the people might starve.

A. Until

B. Before

C. Unless

D. If only

2. Mary has long had the desire _______ a famous writer even though the study of writing would require years of sacrifice on her part.

A. for becoming

B. to become

C. of becoming

D. becoming

3. This is so difficult a problem that the scientist is known to _______ on it for about ten years, but hasn’t found a solution yet.

A.have worked

B. have been working

C.be working

D. work on

4. A majority _______ collectively may be regarded as a being whose opinions and, most frequently, whose interests are opposed to those of another being, which is styled a minority.

A. taking

B. takes

C. take

D. taken

5. I would have passed the college entrance examinations _______ I missed some of the questions and gave the wrong answers.

A. but

B. because

C. as

D. in that

【答案及解析】：

1. Cunless“除非”，从主从句的逻辑关系上看是惟一正确选择。句意：“假如发生了水灾或地震，且火车、汽车又无法通至灾区，除非用飞机空投，否则那里的人们就会饿死。”

2. Bto become在句中做desire的定语，意为“成为一个著名作家的愿望”，其他结构一般不做desire的定语。

3. B不定式to have been working…做主语scientist的补足语，用完成进行式表示：“这个科学家已对如此复杂的问题研究了大约十年，并且还要继续研究下去。”

4. Dtaken在句中做后置定语，修饰majority, 由于与所修饰的词是动宾关系，所以应用过去分词，a majority which is taken collectively可以理解为“(把)大多数人作为一个整体”。

5. A句中but表示转折，后面陈述的是事实情况：“……看错了问题所以没答对”。暗指“若不是看错了题，就会答对而且通过考试”。因此句子前半部分用的是虚拟语气would have passed。