The correct answer is: A. effective drainage.
Camber is a slight slope in the road surface that runs from the center to the sides. It is designed to help water flow off the road and prevent it from pooling in the middle of the road. This helps to keep the road surface safe and free of ice and snow, and it also helps to prevent accidents.
Option B is incorrect because camber does not counteract the centrifugal force. Centrifugal force is the force that pushes objects away from the center of a circle when they are moving in a circular path. When a car is driving around a curve, the centrifugal force pushes the car outward. The camber of the road helps to counteract this force by tilting the road surface slightly inward. This helps to keep the car from veering off the road.
Option C is incorrect because camber does not have anything to do with sight distance. Sight distance is the distance that a driver can see ahead of them. It is important for drivers to have good sight distance so that they can see potential hazards and react accordingly. The camber of the road does not affect sight distance.
Option D is incorrect because camber is indeed provided for effective drainage.