单项选择题
Scale and dirt accumulation in the waterside of a lube oil cooler will be indicated by a gradual increase in the lube oil（）.
A.TBN number B.viscosity C.temperature D.foaming
单项选择题 The lower section of a piston is called the （）.
单项选择题 The diesel engine valve subjected to most severe conditions of service is the （）.
单项选择题 A piston in a four-stroke/cycle diesel engine makes four strokes during each （）.
