Final answer:
The correct direct object pronoun to complete the sentence is 'la'.
Step-by-step explanation:
In the given question, the correct direct object pronoun to complete the sentence 'Marc préfère cette voiture noire?' would be la. The pronoun 'la' is used because 'cette voiture noire' is feminine. Therefore, the correct response to complete the conversation would be 'Oui, il la préfère.'
Learn more about Direct object pronouns in French