当主句的主语和从句的主语一致时且谓语动词为be

当主句的主语和从句的主语一致时且谓语动词为be，常省略从句的主语和be 动词.

省略的条件: (1)从句中被省略的主语必须与主句的主语一致,或者是it；(2)谓语动词必须含有be；(3)从句必须与主语和be动词一起省去，不可只省略主语而保留整个谓语，也不可只保留主语而省略谓语。

1. 由when/while/as/once/whenever/as soon as引导的时间状语从句

例：Please come here as soon as（it is）possible.

While （I was——walking in the rain, I heard my name called. 我在雨中漫步时，听到有人叫我的名字。

由if/unless引导的条件状语从句例：She won’t come to party unless（she is）invited.由though/although/even if/even though引导的让步状语从句

例：He is very good at painting, though（he is）very young. T

hough（he was）exhausted, he stayed up late. 尽管疲惫不堪，他仍很晚才睡。由because引导的原因状语从句

例：He was praised because （he was）brave.

5. 由wherever/where引导的地点状语从句

例：Fill in the blanks with articles where（it is）necessary.

从句和主句中相同或大体相同部分都可以省略

例：The sooner, the better. 越早越好。

She is as tall as I. 她和我一样高。

由as if/as though/as 引导的方式状语从句

例：The boy looked as if（he was）afraid of nothing.

I wonder why he didn’t do as（he was）told to.

比较状语从句省略相同的部分：

例：She likes reading better than (she likes) going to parties.

He has lived here longer than I (has lived).

In winter it is colder in Beijing than（it is）in Guangzhou.