【ago】Agosince和for有什么去别呀?

【ago】Agosince和for有什么去别呀?

【答案】 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.
　　(我现在已不在这里工作.)
　　I have worked here for many years.
　　(现在我仍在这里工作.)
　　小窍门：当现在完成时+一段时间,这一结构中,我们用下面的公式转化,很容易就能排除非延续动词在完成时中的误使.
　　1) (对) Tom has studied Russian for three years.
　　= Tom began to study Russian three years ago,and is still studying it now.
　　2) (错) Harry has got married for six years.
　　= Harry began to get married six years ago,and is still getting married now.
　　显然,第二句不对,它应改为 Harry got married six years ago.或 Harry has been married for six years.
　　4.since的四种用法
　　1) since +过去一个时间点 (如具体的年、月、日期、钟点、1980,last month,half past six).
　　I have been here since 1989.
　　2) since +一段时间+ ago
　　I have been here since five months ago.
　　3) since +从句
　　Great changes have taken place since you left.
　　Considerable time has elapsed since we have been here.
　　4) It is +一段时间+ since从句
　　It is two years since I became a postgraduate student
　　ago表示“...之前”,是过去时的标志
　　since表示“自从...开始,（就已经...)”则是现在完成时的标志
　　for 则像上面所说,可以用于过去时和完成时

这个问题我还想问问老师呢