Answer and Explanation:
This question is about "Pygmalion"
Act III presents the moment when Eliza, after being trained by Pickering and Higgins, presents herself in high society. Although she exhibits very admirable behavior and speaks with impeccable diction and pronunciation, she ends up revealing her true nature when talking about the family and leaving the subject to which she had been taught. This develops the theme, as it shows that we have not been able to change who we truly are, with a new "outfit" and beautiful words, as our true nature will always reveal itself, when we least expect it.