单项选择题
A.facilitate bi-directional operation
B.provide the greatest pump efficiency
C.prevent pump clogging from marine growth
D.prevent cavitation at the pump outlet
单项选择题 In a diesel engine cooling system, the high temperature alarm contact maker will be activated on excessively high water discharge temperature from the （）
单项选择题 In a diesel engine, a cylinder liner should be replaced if it is （） Ⅰ.Scuffed Ⅱ.Scored
单项选择题 Under normal conditions, the main source of crankcase oil contamination is attributed to （）