since和for后面的时态

　　for和since的用法区别：

　　Since +时间点，具体时间。

　　“自从、、、、以来，从、、、以后” 用来说明动作起始时间

　　I have been in Beijing since 2010.

　　For + 时间段，用来说明动作延续时间长度，因此句中的谓语动词，也应该是延续性动词。

　　I have been in Beijing for one year。

　　We have learnt English for about three years.

　　I have been here for 3 days. (对)

　　I have arrived here for 3 days.（误）