单选题In a diesel engine, exhaust valves open before the intake ports are uncovered to （） Ⅰ.reduce pumping losses Ⅱ.reduce back pressureAⅠonlyBⅡonlyCbothⅠand ⅡDneitherⅠnor Ⅱ
单选题
In a diesel engine, exhaust valves open before the intake ports are uncovered to （） Ⅰ.reduce pumping losses Ⅱ.reduce back pressure
A
Ⅰonly
B
Ⅱonly
C
bothⅠand Ⅱ
D
neitherⅠnor Ⅱ
参考解析
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