In the passage, the author observes that Pinker acknowledges rationality as being both "a cognitive and moral virtue." Nevertheless, the author highlights that Pinker's book does not extensively delve into this "profoundly important" association between rationality and morality. By referencing the ancient Greek philosophers who, as per the text, subtly investigated the correlation between moral character and rationality, the author suggests that Pinker's work could gain from a deeper examination of the ethical aspect of rational conduct. Option (C) aptly conveys this notion, as none of the other options accurately encapsulate the intention behind mentioning the Greek philosophers.
So, the correct option is (C): reveal gaps in Pinker's discussion of the importance of ethical considerations in rational behaviour.