Mom, the telephone is ringing. I guess either you or Dad           on the phone.

Waste paper mustn’t _______. We should keep our environment clean.

—When _________ the car _______ ?—Sorry. I don’t know.

Don’t worry. The children always work hard and the teachers _______ in class.

--- It’s difficult for the village children to cross the river for school. --- I think a bridge ________ over the river.