单项选择题

Scientists have spent years_________ into the effects of certain chemicals on the human brain with no results.

A．studying
B．investigating
C．researching
D．inspecting
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单项选择题
The basic causes are unknown, although certain conditions that may lead to cancer have been_________
A．notified
B．qualified
C．identified
D．satisfied
单项选择题
Of all the soldiers they had the _________ of being the fiercest, the most patriotic and the toughest.
A．recognition
B．reservation
C．reputation
D．recreation
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