Answer to Question 1
D
Answer to Question 2
After the Big Bang the universe was filled with only radiation. It was a radiation dominated universe. After protons and neutrons formed the universe was opaque to radiation. Photons couldn't travel far without interacting with an electron. So nothing was visible. At the time of the decoupling, the universe become transparent to radiation and photons could travel with scattering off electrons except at very specific wavelengths. The artifact of this period of decoupling, when photons were first able to travel great distances, is the 3 K cosmic background radiation.
