单项选择题

Which of the following does NOT characterize a normal patent

A．some extension of life span
B．some duration of validity
C．some form of reward
D．some kind of monopoly
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单项选择题
A dead patent is one that ______.
A．no longer wins money
B．has expired
C．is plagiarized
D．is violated
单项选择题
An inventor can generally make a big profit if he ______ his or her invention.
A．publishes
B．keeps secret
C．patents
D．sells
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