单项选择题

Although lube oils used in the main lubricating service systems should have a relatively high flash point to avoid ignition, they can create smoke and fire hazards when they（）

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

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单项选择题

Compensated flow control or constant flow valves are used in hydraulic systems to（）

A.compensate for major leaks in the system
B.maintain the original fluid viscosity
C.allow for changes in pressure and temperature within the system
D.assure constant fluid temperature

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 （）

A.ground the board
B.avoid reversing the polarity of the leads
C.isolate sensitive components with heat sinks
D.all of the above

单项选择题

The heated feedwater entering any flash chamber of a flash-type evaporator will（）

A.vaporize, with the unflashed water remaining at the temperature at which it entered the flash chamber
B.vaporize, with the unflashed water equalizing to the saturation conditions existing in the flash chamber
C.vaporize, with the remaining water at the temperature greater than it entered the flash chamber
D.boil, allowing steam bubbles to rise through the brine at the bottom of the flash chamber