状语从句的压缩的语法

所谓状语从句的压缩,是指把状语从句的某些成分省略掉.例如：
一,把when 引导的时间状语从句压缩为一个现在分词短语（主动的动作）或过去分词短语（被动的动作）.请看例句（括号内是可以省略的部分）：
1.When (I am) helping others,I feel happy.在帮助他人时,我感到快乐.
2.When (I am) asked to help others,I never hesitate.在别人有求于我时,我从不犹豫.
如果when 引导的时间状语从句是一个“主系表”句型,则省略主语和系词：
3.When (it is) possible,people should use renewable energy instead of fossil energy.只要有可能,人们应该使用可再生能源以代替矿物能源.
4.When (it is) necessary,you can call me for help.必要时你可以打电话找我求援.
二,if 引导的条件状语从句也可以用这些方法压缩,请看例句：
5.If you have enough money,you can buy a new house here.If (you do) not (have enough money),to buy a secnd-hand house is also an alternative.如果你有足够的钱,你可以在这里买一所新房.如果没有,买一所二手房也是一种替代方法.
6.I will go to see you tomorrow if (it is) possible.如果有可能,我明天去看你.
三,使用“分词独立结构”,可以把状语从句的连词都压缩掉.请看例句：
7.Weather permitting (= If the weather permits),we'll go picnicking tomorrow.如果天气允许,我们明天去野餐.
8.The river having risen in the night (= As the river had risen in the night),the crtossing was impossible.因为夜间河水上涨了,过河是不可能了.