安全生产奖罚必须以事实为依据，达到鼓励先进、鞭策后进目的。
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Exhaust valve openings in a diesel engine cylinder head are made as large as practical to （）
A. increase back pressure during the exhaust process
B. facilitate periodic replacement of the valves
C. reduce the pumping loss associated with scavenging
D. reduce tension on valve spring
离心式式泵吸入室结构主要有三种：（）吸入室、圆形吸入室、半螺旋形吸入室。
根据水文和气象统计资料，某水域常年波高为0.3m-0.49m，波长为4.5m-5.0m，滩上流速为4.5m/s-6.0m/s。该水域属于（）级航区（）航段。
A. B；J1
B；J2
C；J1
D. C；J2
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