问题

Every possible means _____ to prevent the air pollution, but the sky is still not clear. [ ]

A: is used
B: are used
C:/T
D: have been used

正确答案是：

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It’s difficult for girls _____ soccer well.

Peter is so ___ that he won’t change his mind; we’d better give up the idea.

We always make a card for Mr Wu ________ Teachers’ Day.

Cave exploration, which has come to be known in recent years, is a ________ new sport[ ]