单项选择题
The function of a centrifugal pump double volute casing is to （）.
A.reduce radial thrust to the impeller B.double the liquid velocity through the pump when compared to a single volute C.reduce hydraulic end thrust D.provide the effect of multi-staging
单项选择题 Dirt should not be allowed to contaminate a grease lubricant because the （）.
单项选择题 The presence of bubbles in a refrigeration system liquid line may （）.
单项选择题 Air entering an air-cooled refrigeration system is indicated by （）.
