-Must I send my uncle an e-mail now, Dad? -No, you ____.You____ do that after you finish your homework.

Trees ____ fight air pollution．They are natural air conditioners．

The weather turned out to be fine yesterday. I ______ the trouble to carry my umbrella with me.

 －Are you coming to the English evening?－I’m not sure. I     go to the concert instead.

"Those responsible for the accident      be punished while those contributing to solving the problems be rewarded," promised the official then and there.