单项选择题
Which one of the followings may not be checked before engine starting?（）
A.tank level B.Various filters C.Drains D.seawater temperature
单项选择题 The is employed to warm up a large diesel engine before its starting（）
单项选择题 In slow speed two-stroke engines,（）the fresh air entering begins when and stops as（）
单项选择题 Usually we take the cooling effect of the air flown through the cylinder during the overlap period as（）
