The correct response is "comen; bebe."
Here's why it is correct:
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Ustedes is the second person plural in Spanish (you all), and the verb form that matches this subject is "comen", which is the third person plural form of the verb "comer" (to eat) in the present tense.
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Ana is a singular subject (she), and the appropriate verb form for "bebe," which is the third person singular form of the verb "beber" (to drink) in the present tense.
So, the complete sentences would be: "Ustedes comen arroz con pollo; Ana bebe jugo."