Asatellite in circular orbit around the earth moves at constant speed. this orbit is maintained by the force of gravity between the earth and the satellite, yet no work is done on the satellite. how is this possible?

a. no work is done if there is no contact between objects.
b. no work is done because there is no gravity in space.
c. no work is done if the direction of motion is perpendicular to the force.
d. no work is done if objects move in a circle.