Some frightening pets _________ be kept home so that they won’t hurt others.

—Listen！Helen is singing in the next room.—It _____be Helen .She has gone to Beijing.

 —Tom is in low spirits today. He ______ again in the job interview.—What a pity! He has been greeted with bad luck these days.

If prices rise too high, the government has to do something _________ it. 

The police still haven’t found her, but they’re doing all they      .