1．—I didn't go to work yesterday because my car broke down.
—You ________ have borrowed mine. I wasn't using it then.
答案：could
2．They ________ to win—they've trained hard enough.
答案：ought
3．If you earn more than 3,500 yuan in China, you ________ to pay tax.
答案：have
4．—Sorry, Professor Smith. I didn't finish the paper yesterday.
—Oh, you ________ have done it as yesterday was the deadline.
答案：should
5．—I didn't see her last night at the party.
—You ________ have. But you came too late.
答案：could
6．—Must I return the book a week later?
—Oh, no. You ________.
答案：needn't
7．—She looks unhappy. ________ anything have happened to her?
—I'm not sure, but I guess something may ________ (happen)．
答案：Can; have happened
