公共英语二级辅导：语法讲解（3）

　　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.