My choice is D.
I have read a question in a test and I am very confused about the answer.
They must have come to school, ______?
A. mustn't they B. shouldn't they C. didn't they D. haven't they
I think that A will be the correct answer but the answer in the key is C.
Would you please give me the best choice? Thanks a lot
My choice is D.
I'd use "A".
Good survey question for Tdol.
There appears to be some disagreement on this issue, judging from this thread.
I browsed through Practical English Usage to see if I could find anything, but unfortunately I couldn't find the "definitive" answer (perhaps there is none). The author says on p. 334:
However, mustn't is used in question tags (see 487-488) after must.
It must be nice to be a cat, mustn't it?
However, this sentence is different from the one in the opening post.
***** NOT A TEACHER *****
May I add a few thoughts, not "answers."
1. I think in "real life," many people might say something like: "They must have come to school, [am I] right?"
2. Since this is a test, however, I would also choose "didn't they?" as the "correct" answer.
3. While checking the Web, I noticed that one survey of British speakers indicated that "mustn't" was the favorite.
4. Please consider:
a. You have a car, haven't you? / don't you? (Americans prefer do.)
b. You had a car, hadn't you? / didn't you? (Americans prefer did.)
5. Let's say that the word "must" did not exist. How would we express that idea?
I think (repeat: think) that we would have to say something like:
They had to have come to school, hadn't they? / didn't they? (Again, maybe Americans might prefer did.)