单项选择题
High-speed rotating in a centrifugal purifier can produce a force （） larger than the force of gravity.
A.many thousand times B.between times C.one time D.at times
单项选择题 Here some oil in the oily water separator, as a result of its lower （）, will separate and rise into the oil collection space.
单项选择题 Heat energy is a source of power, but （） will cause damage to the engine.
单项选择题 Head tank should be used to remove （） from cooling water.
