以it is、there is 或there are(或这些表式的其他时态)开头的句子,我们称为“虚主词结构”。 当我们想要强调句子动词后面的观念时,含有虚主词的句子就可以发挥作用。 例如:
Two tall trees were in front of the house．
There were two tall trees in front of the house．
这两个句子提供同样的信息,但是强调的重点不同。 第一个句子强调树木的位置,因为读者阅读的时候,会自然的强调in front。 第二个句子,则比较强调“两棵树”这个观念。
如果以虚主词开头的句子包含一个关系子句或名词子句,则省略虚主词结构,并把子句中的动词当作句子的主要动词,通常会使句子变得较为简洁。 再看几个例子:
劣:There are several methods that have been proposed for selecting the fittest individuals．
佳:Several methods have been proposed for selecting the fittest individuals．
劣:It is clear from the data that raising the temperature led to an increase in the deposition rate．(www.xing528.com)
佳:Raising the temperature clearly led to an increase in the deposition rate．
佳:The data clearly show that raising the temperature led to an increase in the deposition rate．
以it should be noted 或it can be observed 开头的句子常常可以用祈使语气来改写,使句子变得较为简洁:
冗长:It should also be noted that …
简洁:Note that …
冗长:It can be observed that …
简洁:Observe that …
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