If与since的时态

主句为一般将来时态，if从句用一般现在时态：if 主将从现（这个比较好记）

since：（如果能够记住例句的话会比直接记语法更好用）

(1)接时间点：如 I have stayed in that country since 1995. 要求：谓v.用现在完成时，而且须是延续性动词。

(2)接一段时间 + ago：如 They have lived in that house since two years ago. 要求：谓v.用现在完成时，而且须是延续性动词。

(3)接时间状语从句：如 I have loved her since I met her last time. / Lily has stayed at home since she left school. 要求：主句的谓v.用现在完成时，而且须是延续性动词从句的谓v.用一般过去时，而且须是终止性动词。