11.12 比较since和for
 
  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.





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