Correct answer:
B. Les aconsejo que vean la catarata
Both nos and les are indirect object pronouns. Nos is the indirect object pronoun for the first person plural and les is the indirect object pronoun that matches the formal you (ustedes). Recall that an Indirect Object Pronoun is a person that receives the action of a verb indirectly. Its purpose is to tell you to whom or for whom something is done. On the other hand, vean is the conjugation of the verb ver that matches the formal you (ustedes) in the simple present. Finally:
- ¿Qué nos aconsejas que hagamos?
(What do you advise us to do?)
- Les aconsejo que vean la catarata.
(I advise you to see the cataract.