比較since和for

Since 用來說明動作起始時間，for用來說明動作延續(xù)時間長度。 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 作為時間狀語的句子都用現在完成時。 I worked here for more than twenty years. (我現在已不在這里工作。) I have worked here for many years.　 (現在我仍在這里工作。)

小竅門：　當現在完成時+一段時間，這一結構中，我們用下面的公式轉化，很容易就能排除非延續(xù)動詞在完成時中的誤使。 1)　(對) Tom has studied Russian for three years. = Tom began to study Russian three years ago, and is still studying it now. 2)　(錯) Harry has got married for six years. = Harry began to get married six years ago, and is still getting married now. 顯然，第二句不對，它應改為 Harry got married six years ago.　或 Harry has been married for six years.