Final answer:
The skier's deceleration on horizontal ground is caused by the frictional force. The correct answer is a) Frictional force.
Step-by-step explanation:
The force responsible for the skier's deceleration after landing and sliding along horizontal ground before coming to a stop is the frictional force.
This force opposes the motion of the skier and acts parallel to the surface the skier is sliding on. While other forces such as gravitational force, normal force, and tension force exist and act on the skier, it is the frictional force that directly causes the skier to decelerate and eventually stop moving.
The gravitational force acts vertically downward, the normal force acts vertically upward, and tension would only apply if an external object were pulling on the skier.
The force responsible for decelerating the skier is the frictional force.
After landing, the skier slides along a horizontal ground. Friction between the skier's skis and the ground opposes the skier's motion, slowing them down until they come to a stop.