how long have there been mice in your attic?
问题描述：
how long have there been mice in your attic?
—————————————————————————————— two months.
用for或since回答
答
【There have been mince in my attic for】 two months
我的阁楼上有老鼠已经有两个月了.
for two months 这是现在完成时的时间状语.为什么用there have呢因为问句是 have there been，答句要改成陈述语序，也就是there have been。there have been 是 there be的现在完成时态。