I don't remember___________ to the airport that year.
John promised his doctor he _____ not smoke and he has never smoked ever since.
According to the air traffic rules, you ___ switch off your mobile phone before boarding.
When I was young, I was told that I ______ play with matches
-What sort of house do you want to have? Something big?--Well, it ______ be big--that's not important.
Although this ____ sound like a simple task, great care is needed.