A car travels on a banked circular curve at constant speed. All four of the car's tires roll without slipping. The car moves at just the right speed so that the frictional force is zero. Which statement is true?

a. The vertical component of the normal force acts toward the center of the circle.
b. The horizontal component of the normal force acts toward the center of the circle.
c. The normal force acts in the opposite direction as the car's velocity.
d. The normal force acts in the same direction as the car's velocity.
e. The normal force acts toward the center of the circle.