单项选择题

You don't know about the difficulty I had______the work then at all.

A．done
B．to do
C．for doing
D．in doing
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单项选择题
The Internet has brought______big changes in the way we work.
A．about
B．out
C．back
D．up
单项选择题
Charles Babbage is generally considered______the first computers.
A．to invent
B．inventing
C．to have invented
D．invented
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