I guess Professor Wang hasn't finished grading the papers yet. If he had, he would not keep us in （）.

As a senior student, you are supposed to know better than just （）until the examination time.

A.fooled around
B.to fool around
C.having fooled around
D.to have fooled around

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We can derive great pleasure ( )our studies.

A.of
B.to
C.from
D.in

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