Which of These Was a Contribution of Newton to Astronomy

Multiple Choice

Which of these was a contribution of Newton to astronomy?

A) Artificial satellites could be put into orbit about the Earth.
B) The Sun's gravity is greatest on a planet at perihelion, so the planet must speed up.
C) The Moon pulls as strongly on us as we do on it.
D) His differential calculus lets us calculate planetary motions more accurately.
E) All of these were due to Newton's work.