单选题The fresh air coming in through the inner air ports, is compressed by（） to a higher pressure.Athe cylinder headBthe cross-headCthe moving pistonDthe stationary piston
单选题
The fresh air coming in through the inner air ports, is compressed by（） to a higher pressure.
A
the cylinder head
B
the cross-head
C
the moving piston
D
the stationary piston
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