句型24.

If +necessary / impossible/ important等，＋主句.(注意：if与形容词之间的it is被省略。)如：

If necessary, I will do it. 如果有必要的话，我来做此事。


句型25.

主句＋in case+从句.（in case表示以免）如：

I will take my raincoat in case it rains.我要把雨衣带上以免下雨。


句型26.

主句＋due to / because of / owning to / + the fact that +从句。如：

He did not come to school because of the fact that he was ill.由于他有病了，所以没有来上学。



句型27.

When / While / As +从句，＋主句.如：

When I was in the country, I used to carry some water for you.当我在农村时，我常常给你打水。


句型28.

主句＋after / before +从句.　如：

They hadn't been married four months before they were devoiced.他们结婚不到四个月就离婚了。