Answer :
Answer: 4 million years ago.
Explanation: Generally speaking, the more recently two species have diverged from a common ancestor, the more closely related they are.
After two species have diverged from the each other, they are usually no longer able to mate with each other to produce viable offspring. Over generations, mutations within these two species result in them becoming more and more evolutionary distant due to mounting differences in their genomes. As a result, the more recently two species diverge from each other, the closer related they are because there is less time for mutations to accumulate and increase their differences.
Since the most recent time choice offered in the answers is 4 million years ago, this would be where two species that have a common ancestor at this time point would be the most closely related.
