A Stable Nucleus Contains Many Protons Very Close to Each

A stable nucleus contains many protons very close to each other, all positively charged. Why do the protons not fly apart due to mutual Coulomb repulsion?

A) An attractive nuclear force in the nucleus counteracts the effect of the Coulomb forces.
B) The neutrons in the nucleus shield the protons from each other.
C) The Coulomb force does not operate within nuclei.
D) The gravity of the protons and neutrons overcomes their repulsion at such close distances.
E) There are an equal number of electrons in the nucleus which neutralize the protons.