I think the answer is C.
In his experiments with gravity, Isaac Newton showed how the motion of each planet in the solar system results from the combined gravitational pull of the Sun and of all the other planets, each contributing according to their mass and distance from the others.
A. of all the other planets, each contributing according to their
B. of all the other planets, with each of them contributing according to their
C. all the other planets, each of which contributing according to its
D. all the other planets, each contributing according to its
E. all the other planets, each of which contribute according to their
C is my answer because "C" is saying that each planet of all the other planets contributes according to its mass and distance from the other peer planets. Anybody feel me on this?