单项选择题

This hypothesis states that environments that are too clean may actually make the ______ system develop oversensitive responses.

A．mental
B．nervous
C．immune
D．physical
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单项选择题
The violent ______ of his youth reappeared and was directed not only at the army, but at his wife as well.
A．impatience
B．character
C．temper
D．quality
单项选择题
The fruit ______ more than half the country's annual exports, according to a recent report.
A．accounts for
B．stands for
C．provides for
D．makes for
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