Everyone _____ do his best to make the world safe and clean.
Mr. Black has been teaching English in a middle school _____ he came to China.
. — What's that noise?—Oh , I forgot to tell you. The new machine ________
—Sorry. I didn’t break the plate______.—It’s OK. Don’t worry about it.
_____ your classmates and you will make more good friends.
—What’s the matter with you, Sandy?—I’m _____ a bad cold. I think I am dying.