单项选择题
Marine four-stroke diesel engines are mainly （）.
A.of crosshead type B.of trunk piston type C.of low speed type D.all the above
单项选择题 Main bearings are required to support the crankshaft at each （）.
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 （）.
