What event made it possible for photons to begin to travel freely through the universe when the universe was about 380,000 years old?
A. The universe had expanded and cooled enough for electrons to combine with nuclei to form neutral atoms.
B. Atoms started to combine to make the first molecules.
C. Magnetic fields had weakened to the point that they no longer interfered with light.
D. Atomic nuclei were finally able to escape the plasma of the early universe.
E. Fusion of hydrogen to make helium ceased.