【问】 ×He has joined the Army for two years.

他参军两年了。

自从我初学英语的时候起，老师就告诉我这个句子是错误的。但我直到现在也没有弄明白它究竟错在什么地方。

【答】 要弄清这个问题，必须懂得英语的所谓持续动词(durative verbs)和瞬间动词(momen-tary verbs)。持续动词表示在一段时间内延续的动作或事件，例如be，lie，stand，sit，live，work，remain，hold等;瞬间动词表示在极短的时间内完成的动作，例如，come，go，arrive，join，jump，kick，begin，stop等。第一类动词可与表示时间段(a period of time)的时间状语(for two years等)连用，而后一类动词却不能与表示时间段的时间状语连用。请对比：

1. He has been ill for four days.

他病了四天了。

×He got ill for four days.

×He has fallen ill for four days.

2. He has been in the Army for two years.

他参军两年了。

×He has joined in the Army for two years.

3. He has lived there for three years.

他在那里住了三年了。

×He has arrived there for three years.

4. He has been married for four years.

他结婚四年了。

×He has married for four years.

5. I sent it to him a week ago.

我一周前已把它寄给他了。

×I have sent it to him for a week.