The best answer for the dialogue is "Y tú".
In the dialogue, the adult responds with "Más o menos, gracias" to the young person's greeting. This indicates that the adult is feeling neither very good nor very bad. Following this response, the appropriate question for the young person to ask would be "Y tú", which means "And you" in English. This question allows the young person to inquire about how the adult is feeling, continuing the conversation in a polite and conversational manner.
The other options, "Qué bien", "Cómo estás", and "Y usted", are not the best answers in this context. "Qué bien" means "How good" and does not directly relate to the adult's response. "Cómo estás" means "How are you" and is not the best option because the young person should acknowledge the formality of the adult's response by using "usted" instead of the informal "tú". Lastly, "Y usted" means "And you (formal)" and does not match the level of formality used by the young person in the initial greeting. Therefore, "Y tú" is the most appropriate response to maintain the conversational flow and politeness in this dialogue.
