Answer:
b. The horizontal component of the normal force acts toward the center of the circle.
Step-by-step explanation:
When a car on a banked turn move with just the right speed so that the frictional force is zero, a component of the normal force -which is always perpendicular to the surface- acts as the centripetal force on the car. This is because the normal force now has a horizontal component, and this component supplies the centripetal force.