单项选择题

Only after ______ made hundreds of experiments ______ succeed in solving the problem.

A．they had; did they
B．had they; they did
C．they had; they did
D．had they; did they
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单项选择题
______ are willing to work in the factory.
A．John and I myself
B．John and myself
C．I myself and John
D．I and John
单项选择题
--You needn't worry about such ______ as this. --But I just can't forget it.
A．an accident
B．an incident
C．matters
D．things
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