What Was the Significance of the End of the Era

Multiple Choice

What was the significance of the end of the era of nucleosynthesis, when the universe was about 5 minutes old?

A) It marks the time at which the first stars formed.
B) The basic chemical composition of the universe had been determined.
C) The proportions of dark matter and luminous matter had been determined.
D) It marks the time at which the expansion of the universe had settled down to its current rate.