单选题A piston is at bottom dead center when it is（）Aopening the exhaust portsBclosing the fuel portsCfarthest from the cylinder headDnearest to the cylinder head
单选题
A piston is at bottom dead center when it is（）
A
opening the exhaust ports
B
closing the fuel ports
C
farthest from the cylinder head
D
nearest to the cylinder head
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