Even students of average intelligence ________ become top students by improving their study habits.

All of us must do_______ to help protect the environment，or we will have more hazy weather雾霾天气.                                    

Why______ you do everything as if you have to win?

— Mum, my friends are waiting for me outside. May I go out to play with them?— Yes, you        , but be careful, please.

--- You needn’t take an umbrella. It isn’t going to rain.--- Well, I don’t know. It ______do.