The correct answer is A. Gravitational force.
A satellite goes on moving along its orbit round the earth due to the gravitational force of the earth. The gravitational force between two objects is proportional to the product of their masses and inversely proportional to the square of the distance between them. The earth is much more massive than a satellite, so the gravitational force between them is very strong. This force pulls the satellite towards the earth, but the satellite is moving so fast that it keeps falling around the earth instead of falling into it.
B. Centrifugal force is an apparent force that appears to act on objects that are moving in a circular path. It is not a real force, but rather a result of the inertia of the object. The centrifugal force is always directed away from the center of the circle.
C. Centripetal force is the real force that keeps an object moving in a circular path. It is directed towards the center of the circle. The centripetal force can be provided by gravity, tension in a string, or any other force that acts towards the center of the circle.
D. None of these is the correct answer.