Answer
(a) No. (b) Yes. (c) Yes. (d) No.
Work Step by Step
(a) While the speed of the car remains the same, the direction of travel changes. Therefore, the vector quantity of velocity is not constant. (b) As stated in the question, the car has constant speed. (c) Centripetal acceleration is equal to $a_c=\frac{v^2}{R}$. So, since the speed and radius remain unchanged, the magnitude of the acceleration is constant. (d) The acceleration vector always points towards the center of the center of the circle, which varies upon distance. This means that the acceleration direction is not constant.
