--- I think the environment is becoming worse and worse.--- Yes, I really don’t know we can do about it.
He commanded that all the gates _____when it was getting dark in case thieves came in .
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.