Ⅰ.单句语法填空
用恰当的情态动词完成下列句子
1．As a doctor，you should/ought to/must try your best to cure your patients.
2．In some parts of the world，you must/have to boil the water before drinking it.
3．He can't/couldn't have stayed at home this morning.I saw him shopping in another city.
4．You mustn't smoke in this part of the hospital.
5．You ought to/should keep a simple first aid box at home for any accidents.
6．You ought to/should take care of yourself when I'm away.
7．—You ought to/should have finished the article.The deadline is last Friday.
—Sorry.I have been busy these days.Could you give me three more days?
