单项选择题
A.Clogged air intake falters
B.Piston blow-by
C.A defective after-cooler
D.Faulty exhaust valves
单项选择题 Lubricating oil systems for diesel engine journal bearings are usually lubricated by which of the following types of lubricating oil systems?（）
单项选择题 The crankcase of many diesel engines are kept under a slight vacuum by the （）.
单项选择题 Fins are installed on the generating tube surfaces in waste heat boilers to （）.