It’s hard to believe that Jack ________ have fought with the policeman.—Yes.If one ________ ask for trouble, it can’t be helped.

Where did you get this book—I picked it up from a second-hand bookshop if you______ know.

Be careful when you cross this busy street. _____, you may get run over by a car.

The air pollution is terrible.—It will be worse_____ we take action to protect the environment.

He is able to ___________ new jokes about the peopleand things around him.