(1) Since + S + 过去式，S + 现在完成式

例：Since he went to senior high school, he has worked very hard.

　　自从他上高中，他一直很用功。

(2) It is + --- + since  S +持续性谓语动词（表否定）

例：It is three years since she lived here. 她已三年不住这儿了。

(3) It is + --- + since S + 瞬间谓语动词（表肯定）

例：It is years since I stopped smoking）．我戒烟已经数年了。