来看啊，英语题

for加时间段．since加时间点

since表示从某个时间点开始，所以后面加的是具体时间，for表示动作延续了多长时间，所以加一段时间（如：a year等）。
I have been a student for eight years.
I have been a student since 2000.
since后面也可以加从句，从句的时态为一般过去时。
I have lived in Hefei since I was born.
用since和for回答的句子用how long提问
How long have you been a student?
For eight years./Since 2000.
for和since前都只能是延续型动词，加了for和since的时间壮语，瞬间动词须改为延续性动词.。

这个题的分类怎么是保险啊？？？？
天

since+时间点 for+时间段

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。
I worked here for more than twenty years.
(我现在已不在这