A Track 1, Track 2 and Track 3 demonstrate that there is no change in velocity; hence, acceleration exists.

B
Track 1, Track 2 and Track 3 demonstrate that there is no change in speed; hence, acceleration exists.

C
Track 1, Track 2 and Track 3 demonstrate that each has a different acceleration because the cars are moving at different speeds.

D
Track 1 and Track 2 demonstrate that there is no change in velocity so acceleration does not exist, but Track 3 demonstrates that the change in the direction of the car results in a change in velocity; hence, acceleration exists.