The scientists are beating their brains, trying to ______ a solution to the problem.

My brother is an actor. He ______ in several films so far.[ ]

In crowded places like_____airports and railway stations,you _______ take care of your luggage.

Tom studies harder this term. _______, he has made great progress in his lessons.

He should have come to join in the thorough cleaning. —He ________, I think. It’s not his turn.