A vs D

Hi Avif, thanks for the question. My understanding of why D is incorrect is because the author doesn't see the discovery as noteworthy because it demonstrates biochemical reactions that are observable. The importance as stated by the author was the contribution to biochemistry and the understanding of the nervous system's development. This was evidenced by the author's mentioning of the Nobel Prize. While the reaction must in some way be observable, otherwise there would be no passage to speak of, this in itself was not the reason for the author's discussion of Rita's work. I hope this helps. Please let me know if you have any other questions!

It's interesting. Because of your reasoning that the importance was due to the contribution of biochemistry I thought that D was a better answer than A. A was specifically referring to the nervous system while D seemed to be more broad and could include a larger range of biochemistry discoveries.