单选题During the valve overlap period, the exhaust pressure of a turbochargers, four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure （）Aeffective cylinder scavenging and coolingBconstant pressure from the turbochargersCcooler operation of the exhaust systemDeffective constant pressure for turbocharger operation
单选题
During the valve overlap period, the exhaust pressure of a turbochargers, four-stroke/cycle diesel engine must be less than the intake manifold pressure to ensure （）
A
effective cylinder scavenging and cooling
B
constant pressure from the turbochargers
C
cooler operation of the exhaust system
D
effective constant pressure for turbocharger operation
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