单选题During which of the listed piston stroke of a four-stroke/cycle diesel engine, is the piston moving downward?（）AIntake strokeBCompression strokeCExhaust strokeDPumping stroke
单选题
During which of the listed piston stroke of a four-stroke/cycle diesel engine, is the piston moving downward?（）
A
Intake stroke
B
Compression stroke
C
Exhaust stroke
D
Pumping stroke
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