你好,你没有搞懂这些句子的用法:
在这两个句子中,因为都没有时间状语的修饰,所以句子发生的时间不确定,答案也不确定,请你看以下的句子,
They must have been to the USA,haven't they?
He must have been to the USA,hasn't he?
这两个句子都是对的,因为都没有时间状语,可以翻译为:
他(们)到过美国,是吗?
但是加一个状语则变为以下的两个句子:
They must have been to the USA last year,weren't they?
He must have been to the USA last year,wasn't he?
因为,这两个句子都表示去年去了美国这个具体的时间发生的事,所以要用一般过去时态.
又如下面的这个句子:
It must have rained last night,didn't it ?
It must have rained ,hasn't it?