I have lived here (for) five years. 这里的for为什么可以省略?

问题描述:

I have lived here (for) five years. 这里的for为什么可以省略?
Ihave studied English (for) five years.

应当记住,这是一个语法内容:在肯定句中表示一段时间或距离的for可省略.