单项选择题
An additive used to improve the ability of a lube oil to reduce friction is known as a/an （）.
A.suppressant additive B.dispersant additive C.extreme pressure additive D.viscosity improver additive
单项选择题 The suction - force principle of operation is a typical characteristic of （）.
单项选择题 Air leakage between the shaft and stuffing box packing in a centrifugal pump is prevented by （）.
单项选择题 Tube leaks in the distillate cooler of a two stage flash evaporator will result in （）.
