单项选择题
By far the greatest item of maintenance of the reciprocating air compressors concerns （）.
A.the lubrication B.the cooling C.the moisture separation D.the valves
单项选择题 A compressor should never be stopped （）.
单项选择题 Some （） lying in the starting air lines will give rise to corrosion and can cause water hammer.
单项选择题 During compressors running the accumulated moisture in the separators must be （）.
