单项选择题

It was only after some progress ______ in the use and development of electric current that men began to realize the importance and possibilities of magnetism.

A．was made
B．would have been made
C．has been made
D．had been made
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单项选择题
______ for my illness, I would have lent him a helping hand.
A．Not being
B．Had it not been
C．Without being
D．Not having been
单项选择题
You ______ that letter to James. However, you didn't.
A．ought to write
B．ought to have written
C．should write
D．should be writing
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