This is the best answer. In P3, the author describes the additional information we learned about nerve cells as a result of Levi-Montalcini’s discovery of NGF. This is why the author calls the discovery of NGF a “crucial” development in the history of biochemistry.

There’s no evidence the author finds the most value in the laboratory technique used by Montalcini. This isn’t connected to why the author calls the discovery of NGF “crucial.”

This hypothesis is just one part of the story of how Levi-Montalcini discovered NGF. We have no reason to think the author believes this part of the story is the most valuable aspect of NGF. What reason do you have to think that the author values this aspect of NGF over the additional information about nerve cells discussed in the last paragraph? None.

We have no reason to think the author values the discovery of NGF primarily because NGF can stimulate reactions in organisms. What the author focuses on is the contribution of the discovery of NGF to our understanding of nerve cells. This is why the author calls the discovery “crucial” in the development of the history of biochemistry.

We have no reason to think the author values the discovery of NGF primarily because identified NGF. What the author focuses on is the contribution of the discovery of NGF to our understanding of nerve cells. This is why the author calls the discovery “crucial” in the development of the history of biochemistry. The question isn’t just asking, “What’s something that’s supported?” It’s asking why the author finds NGF noteworthy. The answer relates to the impact of the discovery of NGF and its role in the development of biochemistry. The answer isn’t just, “because the discovery of NGF identified a nerve growth substance.”