1、用how long。How long have you lived here?I have lived here for a long time.在现在完成时出现for+一段时间，谓语动词用延续性动词。

2、当for引导的时间短语用来修饰具有静态意义的动词是常常可以省略。

They lived in China (for) seven years.

3、当for与all开头的名词短语连用时，必须省略for.

She’s been lying in bed all day.