Could you give us some advice about this competition?—If you want to win first prize, your design for the museum must be________.[ ]

As the clock _________ nine, players _________ their positions and the match began.

It was quite a serious accident,________caused by careless driving.

It is _____ he often fails in exams _____ makes his parents worried about him.

Air pollution is getting more and more serious，so we must take action________it is too late