When a horse is pulling a wagon, the force that results the horse to move forward will be the force
A. he is exerting on the wagon
B. the wagon is exerting on him
C. the ground is exerting on him
D. he is exerting on the ground

Hint: Newton's third law of motion is the basis for the solving of this question. The law says that for every action we are doing, there will be an opposite reaction for that. When the horse is pulling the wagon, it will be pushing the ground in the backward direction. This will produce some kind of reacting force in the system. This will help you in answering this question.

Complete answer:
In the case mentioned in the question, when the horse is pulling the wagon, it will be pushing the ground in the backward direction. In accordance with the third law of motion, the ground will exert a forward force which will be of the similar magnitude. As the backward force applied by the wagon is lesser than the force applied by the horse, the wagon will be moving in the forward direction. Therefore the ground will be exerting a force on him in order to make the horse move forward.

Hence the correct answer is option C.

Note:
There are so many practical applications for the third law of motion. One of them is in a jet engine. The jet engine will be developing thrust through action and reaction. The engine will be creating hot exhaust gases which will flow out the back of the engine. In reaction to this, a thrusting force will be produced in the opposite direction.