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單項(xiàng)選擇題

Cross scavenging requires the fitting of （） to prevent air or exhaust gas escape when the piston is at the top of the stroke.

A.a exhaust valve
B.a piston skirt
C.a piston crown
D.an air suction valve

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單項(xiàng)選擇題

Crankshafts of medium speed engines are （） from a single piece of steel.

A.unusually solid welded
B.never be solid forged
C.almost invariably solid forged
D.almost invariably be welded

單項(xiàng)選擇題

Cracks in the cylinders and cylinder covers may （） unequal heating.

A.result from
B.result in
C.give out
D.given from

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