单项选择题
Oil mist detectors are usually used on board to detect oil mist density within （）.
A.the engine crankcase B.the engine scavenge boxes C.drain tanks D.fuel tanks
单项选择题 A viscosity regulator used for an engine is usually provided in order to （） for an engine burning heavy fuel oil.
单项选择题 A manometer is used to measure （）.
单项选择题 "gauge pressure" means（）.
