We began to work in the fields. ____, it started to rain, so we went home.
| A．But | B．However | C．While | D．Yet |
John promised his doctor he _____ not smoke and he has never smoked ever since.
| A．might | B．should | C．could | D．would |
According to the air traffic rules, you ___ switch off your mobile phone before boarding.
| A．may | B．can | C．would | D．should |
When I was young, I was told that I ______ play with matches
| A．wouldn't | B．needn't | C．mustn't | D．daren't |
-What sort of house do you want to have? Something big?
--Well, it ______ be big--that's not important.
| A．mustn't | B．needn't | C．can't | D．won't |
—I can’t find my purse anywhere.
—You __ have lost it while shopping.
| A．may | B．can | C．should | D．would |