现在完成时中是常用“since + 时间点”或者“for + 时间段” 来做时间状语,还有“since +从句(常用一般过去时)”。“since + 时间点”和“for + 时间段”常可以互换使用,意思不变。如:“since three years ago => for three years”。
另外,“since+年代”也是可行的,如since 2002。
试比较这几个句子:
I haven't seen him for three years.
I haven't seen him since three years ago.
I haven't seen him since I met him