In the Very Early Universe, Which of the Following Types

Multiple Choice

In the very early universe, which of the following types of particles and antiparticles first stopped being spontaneously formed out of photons and why?

A) protons and neutrons, because their formation requires a larger number of photons
B) electrons and positrons, because their formation requires a smaller number of photons
C) protons and antiprotons, because their formation requires higher-energy photons
D) electrons and neutrinos, because their formation requires lower-energy photons
E) Protons, antiprotons, electrons, and neutrinos stopped forming at the same time.