The correct answer is: A. stopping distance
The minimum stopping sight distance is the distance needed to stop a vehicle safely. It is equal to the reaction distance plus the braking distance. The reaction distance is the distance a vehicle travels before the driver applies the brakes. The braking distance is the distance a vehicle travels after the brakes are applied.
On a single lane road with two way traffic, there is a risk of head-on collisions. To avoid these collisions, drivers need to be able to see far enough ahead to stop in time if a hazard appears. The minimum stopping sight distance is the distance needed to stop a vehicle safely in this situation.
Option B is incorrect because it is twice the stopping distance. This would not be enough distance to stop a vehicle safely in a head-on collision.
Option C is incorrect because it is half the stopping distance. This would not be enough distance for a driver to react to a hazard and stop in time.
Option D is incorrect because it is three times the stopping distance. This would be too much distance and would not be necessary to stop a vehicle safely in a head-on collision.