导读：Since 用来说明动作起始时间;for用来说明动作持续时间长度。三年级英语中学生不仅要知道单词的拼写方法，也要能够熟练在不同句式中采用不同的写作方式以表现不同的意思，本篇整理了since和for的区别知识，以及since的相关用法，帮助学生做好课堂与课下的复习，三年级学生应该养成主动学习的习惯，课上对老师传授的内容认真理解，课下对知识点勤加搜集，在三年级学习中不断提升自我。

　　Since 用来说明动作起始时间，for用来说明动作延续时间长度。

　　I have lived here for more than twenty years.

　　I have lived here since I was born..

　　My aunt has worked in a clinic since 1949.

　　Some new oilfields have been opened up since 1976.

　　I have known Xiao Li since she was a little girl.

　　My brother has been in the Youth League for two years.

　　I have not heard from my uncle for a long time.

　　注意：并非有for 作为时间状语的句子都用现在完成时。