单项选择题
A.during the valve overlap period
B.with only the exhaust valve open
C.at a pressure below atmospheric
D.without cooling the cylinders or pistons
单项选择题 To prevent vibration damage to the fuel supply line of a diesel engine, you may use （）.
单项选择题 When the prime movers of two paralleled generators are equipped with mechanical- hydraulic governors, and are operating within their designed range, the unit with the least amount of speed droop will （）.
单项选择题 Diesel engine jacket water is used in the distillation process as the （）.