单选题Because the top of the connecting rod swings about the pin and changes direction each time the piston reaches mid-stroke, the relative speed between bearing and pin at mid-stroke is zero, （）to a maximum as the piston approaches top or bottom dead center and then （） back to zero again as the piston approaches mid-stroke and the connecting rod changes direction.Aaccelerates；deceleratesBaccelerates；acceleratesCdecelerates；deceleratesDdecelerates；accelerates
单选题
Because the top of the connecting rod swings about the pin and changes direction each time the piston reaches mid-stroke, the relative speed between bearing and pin at mid-stroke is zero, （）to a maximum as the piston approaches top or bottom dead center and then （） back to zero again as the piston approaches mid-stroke and the connecting rod changes direction.
A
accelerates；decelerates
B
accelerates；accelerates
C
decelerates；decelerates
D
decelerates；accelerates
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