单项选择题
A.has to be cooled
B.has heated
C.has preheated
D.has to be preheated
单项选择题 In large marine diesel engines cylinder oils usually contain additives formulated to impart the （） to clean the rings and grooves.
单项选择题 In general, （） is suitable for delivering small quantities at high pressure.
单项选择题 In four strokes engine, the cycle of events is completed in four strokes of （）.