单项选择题
Propeller pitch speed minus ship speed divided by the propeller pitch speed is termed （）.
A.apparent slip B.tree slip C.pitch D.propulsive efficiency
单项选择题 A multistage centrifugal pump can be BEST described as having （）.
单项选择题 If a refrigeration system compressor crankcase is sweating, you should （）.
单项选择题 Crankcase sweating in a refrigeration system is caused by （）.
