用 must, oughtn't to, don't have to, mustn't, needn't或 have to填空。
1. You _____ go on working because you look so tired now.
2. The weather turned out to be fine yesterday. I ______ have had the trouble to carry my umbrella
with me.
3. If you earn more than ~5,000, you _____ pay tax.
4. You ______ play now ! You shall finish your homework first!
5. You can't give up. You ______ try to get over the difficulties.
