单项选择题
Main bearings are required to support the crankshaft at each （）.
A.end B.web C.pin D.journal
单项选择题 Lubricating oil for an engine is stored at the bottom of the （）, known as the sump or in a drain tank located beneath the engine.
单项选择题 Low compression results from （）.
单项选择题 Low compression of diesel engine may result from （）
