单项选择题
A.open late and close early
B.open late and close late
C.fail to open when the engine is cold
D.fail to open at normal operating temperature
单项选择题 Lubricating systems for diesel engines are usually designed to initially provide lube oil to the engine （）
单项选择题 The expansion tank in a diesel engine closed freshwater cooling system is located at （）
单项选择题 On most modern diesel engines, the main and connecting rod bearings receive their lubricating oil by （）.