They must have been to the USA,have not they?与He must have been to the USA，was not he?区别

Question

最好讲讲为什么句子主语一换，must反义疑问句就不一样了？

Answer 1

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?

Answer 2

这个和主语没有关系
They must have been to the USA,have not they?
严格的说应该是这样的——He must have been to the USA，has not he?
前面没有具体的时间状语，就用完成时。有时间状语，就用一般时。
He must have been to the USA two years ago，was not he?

Answer 3

关于must have been 的反义疑问有个特殊的用法，只能死记硬背。我记得是高三的英语，但一般不会考。可我记得是如果 must have been 句子里有明确的过去的时间，反义疑问句才会用一般过去时，如果没有还是与主句一样。
具体记不清了，问老师吧，这个其实不是重点。。。。