What is best to say about a runner who is running at a constant velocity?

a. their acceleration is positive.

b. their acceleration is negative.

c. their acceleration is zero.

d. their acceleration cannot be determined

Their acceleration is zero. therefore the correct answer is C.

Acceleration is defined as the rate of change of velocity, since the runner is moves with the constant velocity, therefore their will be no change in its velocity with respect to time, or the rate of change of velocity (acceleration) is zero.