69. The research is so designed that once _____ nothing can be done to change it.　

　A. begins　 B. having begun　 C. beginning　 D. begun 答案选D，可视为once it is begun之省略。

68.If _____ carefully, the experiment will be successful.　

　A. do　　 B. does　　 C. done　　 D. doing答案选C，可视为if it is carefully done之省略。

67.　He is a man of few words, and seldom speaks until _____ to.

　A. spoken　　 B. speaking C. speak　　 D. be spoken

此题容易误选B，认为until是介词，后接动词时用动名词形式。其实，此题应选A，until spoken to为until he is spoken to之省略。句意为“他是个沉默寡言的人，别人不同他说话，他很少同别人说话”。按英语习惯，一些表示时间、地点、条件、方式、让步等的状语从句，若其主语与主句主语一致，且从句谓语包含动词be,那么可将从句的主语和动词be省略：

　You must study hard while (you are) young, or you will regret when (you are) old.趁年轻时要努力学习，不然到老了你会后悔的。

I won't go unless (I am) invited. 我不会去,除非请我。

Look out for cars when (you are) crossing the streets.过马路时要注意汽车。

While (I was) waiting I was reading some old magazines.等的时候我在看一些旧杂志。

He worked very hard though (he was) still rather poor in health.尽管身体还不好，但他仍努力工作

He will work hard wherever (he is) sent by the Party.无论党把他派往哪里,他都会努力工作。　

66.They kept trying _____ they must have known it was hopeless.

　A. if　　 B. because　 C. when　　 D. where　

　此题最佳答案为C，when在此的意思不是“当……的时候”，而是“尽管”、“虽然”的意思。又如：He walks when he might take a taxi.尽管他可以坐出租车，但他却走路。He stopped trying when he might have succeeded next time.尽管他本来下次就可以成功的了，但他却停止努力了。The boy was restless when he should have listened to the teacher carefully.这男孩子本来应该专心听老师讲的，但他却坐立不安。

　有许多同学只知道when表示“当……的时候”，而不知道它还有其他许多意思，除上面提到的表示“尽管”、“虽然”外，when还可表示“既然”、“考虑到”。如：Why do you want a new job when you've got such a good one already? 既然你有了这么好的一份工作，你为什么还要找新的工作呢？

65.There are five pairs, but I'm at a loss which _____ to buy.

　A. to be chosen　 B. to choose from　 C. to choose　 D. for choosing

　此题容易误选C，其实应选B。choose表示“选择”，其实是指“选择出来”(pick out)，而不是指“从……选择”，要表示后者的意思，要用choose from，有时也用choose among。同样地，下面两例中的介词from也不可省略：

　Here are some books for you to choose from. 这些书可供你选择。

　There are too many cakes to choose from. 蛋糕太多了，不知要选哪个好。

　比较：　He didn't know what to choose.他不知道选什么。

　　　　　 He didn't know what to choose from.他不知道从哪儿去选。

64. He was not an actor, who often appeared on stage, _____ a writer, writing stories.

A. but　　　 B. and　　 C. then　　 D. so　 答案选A，主要考查not ... but ...结构。

63.Please make my excuse at tomorrow's meeting-I've got too much work _____.

　A. to do to come　　 B. doing coming　 C. to do coming　　 D. doing to come　

　此题最佳答案为A，不定式to do与have got much work搭配，即have got much work to do (有许多工作要做)；不定式to come与much前的too搭配，构成too ... to ...句式，全句意为“我有太多的工作要做，不能来”

62.I don't know whether to stay in teaching or _____ another job.　

　A. trying getting　　 B. to try to get　　 C. trying to get　　 D. try get

　答案选B，to stay in teaching与to try to get another job为两个并列的选择成分，故同用不定式。另外比较：try to do sth=设法做某事，try doing sth=做某事看看有何效果。

61.He just does what he pleases and never _____ about anyone else.

　A. think　　 B. thinks　　 C. thinking　　 D. thought

　答案选B，thinks与前面的does为并列谓语，同用一般现在时。

60.Few pleasures can equal ______ of a cool drink on a hot day.

　A. some 　　B. any 　　C. that 　　D. those

答案解析：：一看到few pleasures，容易错选D.但后面所设条件为a cool drink,因而正确答案应为C.