Final answer:
The correct direct object pronoun to complete the sentence is 'le'.
Step-by-step explanation:
The correct direct object pronoun to complete the sentence is le.
So the correct response to the question 'Tu aimes ce livre?' would be 'Oui, je l' aime.'
In this sentence, 'ce livre' (this book) is the direct object, and since 'livre' is masculine singular, the appropriate direct object pronoun is 'le'.
Learn more about Using correct direct object pronouns in French sentences