单项选择题
A.their free-floating design
B.their relatively small size
C.the reciprocating motion of the piston
D.their position in the lubrication system
单项选择题 Internal combustion engine crankcase vent outlets must be equipped with （）
单项选择题 The interior of some diesel engine saltwater heat exchangers are protected from corrosion by the use of（）
单项选择题 Proper lubrication of the main bearing is more easily obtained in a single acting four-stroke/cycle diesel engine than in a single acting two-stroke/cycle diesel engine because （）