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四冲程柴油机的排气阀定时为:

A、下止点后开,上止点后关
B、下止点前开,上止点前关
C、下止点后开,上止点前关
D、下止点前开,上止点后关
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正确答案:

D

答案解析:

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Questions16to20arebasedonthefollowingpassage:

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