单项选择题
The primary duty of lube oil is to reduce （） between the working parts of an engine.
A.power output B.friction and wear C.indicated pressure D.rated horsepower
单项选择题 The pressurized air is usually cooled to increase the charge air （）.
单项选择题 The pressure of pilot air is usually （） than that of starting air.
单项选择题 The power generated in the turbine must （） that required by the compressor.
