Determine whether the following statements are true and give an explanation or counterexample.

a. If the acceleration of an object remains constant, then its velocity is constant.

b. If the acceleration of an object moving along a line is always 0, then its velocity is constant.

c. It is impossible for the instantaneous velocity at all times a ≤ t ≤ b to equal the average velocity over the interval a ≤ t ≤ b.

d. A moving object can have negative acceleration and increasing speed.