Which of the following is not true?
a. The instantaneous velocity of a particle can be greater than its average velocity.
b. The instantaneous velocity of a particle can be less than its average velocity.
c. If the average velocity of a particle over some interval is equal to zero, the instantaneous velocity of the particle over that interval may not be equal to zero at any time during the interval.
d. If the average velocity of a particle over some interval is equal to zero, the instantaneous velocity of the particle over that interval must be equal to zero at some time during the interval.