Tag question

Neither.

"You must have been to America, mustn't you?"

Clive

What about "haven't you"?

No, the grammar rule is, we must use the same modal word in the tag question. You can't start a tag question with "must" and switch to a different modal in the second part. You must / could / may have done ...- is an assumed thought which in the case should be reenforced by " mustn't you ", as Clive has suggested.

Do you agree the opinion in the link:http://www.EnglishForward.com/English/MustInTagQuestion/hphrb/post.htm?

You have worked a lot. You must be tired, aren't you?

She must be the new teacher, isn't she?

Wow, Robert is a flight attendent, he must fly a lot,

Do you agree the opinion in the link:http://www.EnglishForward.com/English/MustInTagQuestion/hphrb/post.htm ? Only with what GG said.

You have worked a lot. You must be tired, aren't you?

She must be the new teacher, isn't she?

****,
This is how I see you questions.

wangqh2696122You have worked a lot. You must be tired, aren't you?

You have worked a lot lately, haven't you? you must be tired. OK

She must be the new teacher, isn't she? -

CliveYou have worked a lot. You must be tired, aren't you?She must be the new teacher, isn't she?Wow, Robert is a flight attendent, he must fly a lot, doesn't he?

I think these would all be okay if you make the tag question a separate sentence. Clive, do you agree, or is it still considered an improper tag questions?

You must be tired. Aren't

That's what I thought!