After About 2 Seconds, the Early Universe Contained Almost No

Multiple Choice

After about 2 seconds, the early universe contained almost no neutrons. But protons remained. Why this difference?

A) Neutrons are much more massive than protons. After the first 2 seconds the temperature of the universe had fallen below the threshold for pair production of neutrons but not of protons.
B) Neutrons, being uncharged, can get close to other particles and annihilate them. Protons, being charged, cannot get close to other particles.
C) Free neutrons decay spontaneously. Free protons are stable.
D) Virtual proton-antiproton pairs were produced during the inflationary period, but neutral neutrons have no antiparticles and thus were not pair produced.