单项选择题

This mathematic problem was so difficult that no student and no teacher_________ able to solve it.

A．were
B．is
C．was
D．are
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单项选择题
He _________a good knowledge of English by careful study.
A．gained
B．obtained
C．earned
D．acquired
单项选择题
If you have any questions, please go and ask_________.
A．the responsible person for the activity
B．the person responsible for the activity
C．the activity's responsible person
D．the person for the activity responsible
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