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 waswalking in the rain, I heard my name called. 我在雨中漫步时，听到有人叫我的名字。2. 由 if/unless 引导的条件状语从句例：She wont come to party unless（she is）invited.3. 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. Though（he was）exhausted, he stayed up late. 尽管疲惫不堪，他仍很晚才睡。4. 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. 6. 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。7. 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 didnt do as（he was）told to. 8. 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.