What was the major events that happened in the proterozoic period? (it's in the precambrian era)

The Phanerozoic Eon is the current eon in Earth's history. The Phanerozoic began 542 million years ago with the Cambrian explosion and continues to the present. The Proterozoic eon was a period of time during which several different events took place, eventually helping to shape the earth as we know it today. It lasted nearly two billion years, starting 2,500 million years ago to 542 million years ago. During this time, life began to evolve into more complex organisms.

I think it might be A