单项选择题

（）the reactions of people with this drug, scientists have learned more about the brain.

A．By studying
B．To study
C．They study
D．They're studying

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单项选择题
They insisted that we（）a delegation to their country.

A．sent
B．would send
C．send
D．to send
单项选择题
It wasn't（）the tiger was caught and sent to the zoo.

A．before long
B．long before
C．long after
D．long when
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