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

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

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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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