單項(xiàng)選擇題In extreme weather conditions, either hot or cold, control of the air conditioning plant presents () difficulties.

A.few
B.little
C.a little
D.less


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3.單項(xiàng)選擇題In a vacuum distillation system, the case is the higher the pressure, ().

A.the saturation temperature is higher
B.the higher the saturation temperature
C.the higher is the saturation temperature
D.the saturation temperature is more high

4.單項(xiàng)選擇題A hydraulic machine is one that uses () to do work.

A.liquid
B.steam
C.gas
D.electricity

5.單項(xiàng)選擇題If oil density were greater than water’s, the oil separator ().

A.did work
B.would work well
C.didnt work
D.wouldnt work