不定式的完成式、進行式和完成進行式：這三類在考研題中出現的頻率很高，要特別注意不定式的這三種形式

1、如果不定式所表示的動作與主要謂語所表示的動作(狀態)同時(或幾乎同時)發生或發生在主要謂語之后，那么用不定式的一般形式

He received a warm welcome from the Australians and from his family who had flown there to meet him.

In 1967, he arrived back in England, where a quarter of a million people were waiting to welcome him.

After all, eighty was a special birthday, another decade lived or endured just as you chose to look at it.

Now suddenly she began to sob, holding herself in as if weeping were a disgrace.

2、如果不定式所表示的動作(狀態)發生在主要謂語動詞或特定的某時間之前,那么不定式就要用其完成式

She feels relaxed to have finished writing her thesis before the deadline.

33)The Vikings are believed America.

[A] to have discovered[B] in discovering[C] to discover[D] to have been discovered

34)The students were to at the auditorium before 1:30 pm, but the lecture was cancelled at the last minute.

[A] assembled [B] have assembled [C] assembling [D] be assembled

35)He was to the new ambassador, but he fell ill.

[A] having telephoned[B] have telephoned[C] has telephoned[D] telephoning

3、不定式進行式表示主要謂語動詞所表示的動作(情況)發生時,不定式所表示的動作正在發生

When he came in, I happened to be doing my experiment in the lab.

Why do you stand here?You are supposed to be working in the workshop.

4、不定式完成進行式表示其動詞所代表的動作，在主要謂語動詞所代表的動作之前一直在進行

The students from the Department of Sociology are said to have been investigating the possibility of producing the new product.

They are quite happy to have been cooperating harmoniously with us till now.