At What Point Do the Weak Nuclear and Electromagnetic Forces $10^{12} \mathrm {~K} \text {, }$

Multiple Choice

At what point do the weak nuclear and electromagnetic forces split?

A) never, they are still united
B) at $10^{12} \mathrm {~K} \text {, }$ when pair production starts for neutrons and protons
C) at $10 ^{- 43}$ seconds, when all four forces separate as the Planck Era ends
D) at about four seconds, when at millions of degrees hydrogen forms helium
E) after about $10 ^ { - 10 }$ seconds, when the temperature drops below $10 ^ { - 15 } \mathrm {~K}$