单项选择题
The most common cause of lowering the crankcase lube oil flash point is （）.
A.more water contents
B.contamination with fuel oil
C.higher temperature
D.sufficient cooling of oil mist
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单项选择题
The mechanical efficiency of an engine （） because losses occur in the form of friction.
A.is always less than 100%
B.is always more than 100%
C.is always equal to 90%
D.is always less than 90% -
单项选择题
The marine diesel engine is a type of diesel engine used on ships The （） of its operation is not very difficult to understand.
A.principle
B.principal
C.cause
D.case -
单项选择题
The majority of medium speed and high speed marine diesel engines for main or auxiliary drive operate on the （） cycle.
A.two-stroke
B.four-stoke
C.long-stroke
D.short-stroke
