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 known¹ 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) Harry² 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.

1 known   

adj.大家知道的；知名的，已知的

参考例句：

• He is a known artist.他是一个知名的艺术家。
• He is known both as a painter and as a statesman.他是知名的画家及政治家。

2 harry   

vt.掠夺，蹂躏，使苦恼

参考例句：

• Today,people feel more hurried and harried.今天，人们感到更加忙碌和苦恼。
• Obama harried business by Healthcare Reform plan.奥巴马用医改掠夺了商界。