单项选择题

Economics, several courses of which I have taken thus far,（）to be difficult but useful for almost all students。

A.prove
B.havebeenproved
C.proves
D.areproved

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A large crowd（）expected at the football match。

A.is
B.be
C.are
D.will
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The school staff（）gathered to hear the president speak。

A.is
B.be
C.are
D.will
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