单项选择题
Hydraulic machinery failures are commonly caused by contamination of the hydraulic fluid and （）.
A.fluid friction B.fluid turbulence C.component misalignment D.pressure surges
单项选择题 When you adjust a thermostatic expansion valve, （）.
单项选择题 If a centrifugal pump were continually operated with the discharge valve closed, the （）.
单项选择题 A double suction centrifugal pump impeller has been installed in the reverse direction, and will （）.
