for后加一段时间 ,但不能错误地认为for加一段时间就是完成时.同样 since 后加具体过去时间或过去时的句子,如果跟一般现在时时,since 表示“既然、由于”之意.
例 for three days
I have been here for three days.
I stayed there for three days. Now, Iwell remember that time.
I will stay there for three days there, then I will go to Australia.
Since three days ago, I have been here.