Answer:
C
Step-by-step explanation:
The relationship demonstrated by the student using a string and a ball to model the Earth and Sun is the gravitational attraction between the two celestial bodies. Gravity is the force that keeps the Earth in orbit around the Sun, and the strength of this force is proportional to the masses of the two objects and the distance between them. The string represents the gravitational pull between the two objects, which keeps the ball (representing the Earth) in a circular orbit around the larger ball (representing the Sun). Therefore, the correct answer is:
The gravitational attraction between the Earth and Sun.