When the Big Bang Began, All the Fundamental Forces Were

When the Big Bang began, all the fundamental forces were unified and behaved like a single force. As the universe expanded and cooled during the Big Bang, when did the strong nuclear force first become a separate force?

A) at the start of quark confinement, when the universe was about 10^-6 s old
B) when pair production ceased, when the universe was about 1 s old
C) at the Planck time, when the universe was about 10^-43 s old
D) at the start of the inflationary period, when the universe was about 10^-35 s old