三、加深理解非谓语动词的不同时态在句中的用法

1．These reptiles are thought to live among rocks．People think that these reptiles live among rocks．

2．Some dinosaurs are thought to have lived in swamps．People think that some dinosaurs lived in swamps．

注:通过例句1和2各句的转换可以得知“to live”表示现在的情况;“to have lived”表示过去的情况。

3．When you have used the paper cups once，you throw them away．Having used the paper cups once，you throw them away．

注:在例句3中用现在分词的完成式替换了“when”引导的从句。用分词的完成式来说明“use”这一动作发生于主句的谓语动词“Throw”之前。

4．The bridge which is being built across the river is not a suspension bridge．The bridge being built across the river is not a suspension bridge．

注:在例句4中用现在分词的被动形式替换了“which”导引的定语从句,说明现在分词“being built”的动作正在进行。

5．The problem which will be discussed is what laser is. The problem to be discussed is what laser is.

注:在例句5中用不定式的一般式替换了“which”引导的定语从句,说明不定式“to be discussed ”的动作将要发生。通过上面的例子,笔者是想说明,只要在英语学习中能自觉地运用归纳,比较及辨析的方法,就能巩固所学的知识,达到灵活运用的目的。