单项选择题
Shaker, circulation and spray are the three general methods used in（）
A.pre-injection fuel oil treatment B.lube oil filtration C.lube oil purification D.piston cooling
单项选择题 Wristpin bearings are difficult to lubricate because of their oscillating motion and（）
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（）
