Why B is not right?

There is a small difference between answer A and answer B. We are looking for the answer that “may help account for the occurrence of neurogenesis in canaries.” Answer B is the process by which canaries learn songs — but that process doesn’t help ACCOUNT for the occurrence of neurogenesis. It is instead the way in which researchers discovered neurogenesis in canaries. In contrast, the life span of the average canary is described by the passage as “a possible explanation for this continual replacement of nerve cells (lines 40-41) which, of course, is neurogenesis. That is why answer A is correct! I hope that helps. Please let us know if you have further questions.

Thanks for your explanation! Didn't even notice such small difference between A & B when I was doing this one...

@Karry-Jiao great! Let us know if you have any other questions!