单项选择题
A.are exposed to a vacuum
B.come in contact with extremely hot surfaces
C.are reduced in temperature to just above the pour point
D.become extremely agitated or aerated
单项选择题 Compensated flow control or constant flow valves are used in hydraulic systems to（）
单项选择题 To avoid damaging the components of a printed circuit board when testing it with a DC volt-ohmmeter, you should （）
单项选择题 The heated feedwater entering any flash chamber of a flash-type evaporator will（）