单项选择题

The solution, if that is the case, is to install a pressure-reducing ______ on the water system.

A．shaft
B．shelf
C．axis
D．valve
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单项选择题
It can be inferred from the passage that ______.
A．the energy crisis is similar to the natural disasters we had in the past
B．the problem of energy is the most serious problem our country is confronted with
C．the author is uninterested in the problems of our society
D．the author is particularly worried about the crises we are facing
单项选择题
It ______ me to see him in such a bad health. He was such an energetic and strong young manonly several months ago.
A．depressed
B．upset
C．harmed
D．grieved
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