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單項(xiàng)選擇題

The mechanical efficiency of an engine is always less than 100% （） losses occurring in the form friction.

A.because
B.since
C.due to
D.owing to

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The pressure difference before and after the lube oil filter indicates （）the filter should be cleaned.

A.when
B.how
C.where
D.whether

單項(xiàng)選擇題

A diesel engine which is rated for normal operation at a crankshaft speed of 800 RPM, is commonly classed as a （）.

A.slow-speed diesel
B.medium-speed diesel
C.high-speed diesel
D.constant-speed diesel