You’d better put on a heavy coat.Sometimes it________be very cold here at night.

It has been announced that students _______ remain in their seats until all the papers have been collected.

Even a drop of water ______because it is so important to all the living things.

—Look at the sign! —Oh, I see.We _______ waste water.

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