4. Two students have volunteered to explore the galaxy in a spaceship. As they travel through space, they measure the magnitude of the gravitational force between their spaceship and the Earth. They find that the
gravitational force on the spaceship is -
A. proportional to the distance from the Earth
B. inversely proportional to the distance from the Earth
C. proportional to the square of the distance from the Earth
D. inversely proportional to the square of the distance from the Earth