Earth formed about __________ years ago, and the oldest known living organisms date to __________ years ago.
A. 4.6 billion years ago ... 3.5 billion years agoB. 6,000 years ago ... 6,000 years agoC. 13.7 billion years ago ... 4.6 billion years agoD. 3.9 million years ago ... 2.0 billion years ago