Life originated approximately 3.5 billion years ago, and the first multicellular organisms appeared around 2.1 billion years ago.
The earliest animals are dated around 600 million years ago, and from that time most of the phyla were recognizable in the fossils known as Ediacaran biota, named after the Ediacaran period, which was the last period of the Precambrian.
This means d, Ediacaran Period, is the right answer.
