Answer:
The correct answer is Usted/Ustedes.
Explanation:
Unlike English, where the pronoun you can be used for normal or informal conversation, in Spanish there are two different pronouns for each of these situations.
For informal situations we use Tú, and for formal situations we use Usted (Ustedes for the plural).
Next I will write all the pronouns that exist in Spanish:
persona singular plural
1ª yo nosotros, nosotras
2ª tú vosotros, vosotras
3ª él, ella, Ud., ellos, ellas, Uds.
