When the Core of a Massive Star Collapses, a Neutron

When the core of a massive star collapses, a neutron star forms because

A) all the charged particles are ejected in the resulting explosion.
B) protons and electrons combine to make neutrons.
C) iron nuclei disintegrate into neutrons.
D) neutrinos escaping from the core carry away most of the electric charge.
E) the collapse releases a large number of protons, which soon decay into neutrons.