——How long have you lived with your grandparents?——For about three days.答语加不加for?

问题描述:

——How long have you lived with your grandparents?——For about three days.答语加不加for?

应该加介词for表示时间的延续.
不过,不少新闻报道中这个用法中的for偶尔也能省略.不省略最好.