The best response to how the passage develops the topic of Jourdain’s foolishness is:
by revealing that Jourdain knew what prose was without realizing it.
This option highlights Jourdain's lack of awareness about his own speech and its classification, demonstrating his foolishness in thinking that he doesn't engage in prose despite using it in his daily conversation. The exchange underscores his ignorance despite being in a situation that should teach him, thus emphasizing his foolishness.