The correct answer is D. los. Direct object pronouns are used to replace nouns to avoid repetition in Spanish sentences.
The correct answer is D. los. In the sentence '¿quieres ver a tus amigos? Sí, quiero verlos,' the direct object pronoun 'los' is used to replace 'a tus amigos' for 'them.' This is a common practice in Spanish to avoid repetition of the noun.