在使用英语时,有一个规则：能使用短语时不用句子,能用单个词时不用短语.因此,有些从句在实际应用时,有些可以可以简化成短语.下面先讲讲义中出现过的时间状语、原因状语和条件状语的简化情况.
情形一：从句主语和主句主语一致
步骤：去（从句）连词—去（从句）主语—（从句）谓语变分词
时间状语从句
1、 以when,while引导的时间状语从句和以if引导的条件状语从句,谓语动词是主动语态时,如果从句谓语动词所表示的动作是与主句谓语同时发生,可简化为现在分词的一般式；如果从句谓语动词所表示的动作发生在主句谓语之前,则可简化为现在分词的完成式.
When we heard (=When hearing/Hearing)the teacher's pleasant talk to us,we began to feel comfortable.
While Mary was standing(While standing/Standing) in front of the teacher,she(Mary) was very nervous.
状语从句的谓语动词是被动语态时,可简化为过去分词.
When ／If it is heated to a high temperature(=Heated to a high temperature),water will change into steam．
If we are given(=Given) more time,we can do the work better.
If the city is seen(=Seen) from the mountain,it（the city） looks very beautiful.
2、以after,before引导的状语从句可用after,before+从句谓语动词的动名词（短语）形式构成介词短语作状语.
After he put on (=After putting)the trousers,he found they were 2 inches too long.
也可：Having put on the trousers,…
Before we do the job(=Before doing the job),we'd better think it over.
3、以as soon as 引导的状语从句,可用On+谓语动词的动名词形式作状语,此时的动词是非延续性动词.
Doctor Bethune began to operate on the wounded soldiers as soon as he arrived (=On arriving)at the village.
2、原因状语从句
可简化为分词短语作状语.
Since you still look pretty sick(=Looking pretty sick),you'd better have a good rest.
Because he was(=Being) one of the best teachers in the city,he was given a medal.
Since I didn't know Chinese(=Not knowing Chinese),I tried to speak to her in English.
情形二：从句主语和主句主语不一致
步骤：去连词—留主语—动词变分词
当状语从句的主语与主句的主语不一致时,状语从句简化成分词短语时则要保留其本身的主语,使该主语成为分词短语的逻辑主语,即构成独立主格结构（主语+分词）.例如：
As it was fine that day（=It being fine that day））,we decided to go fishing．
Since his father had fallen ill（His father having fallen ill）,John had to begin working at the age of ten.
If weather permits(=Weather permitting),we will have a picnic.
