Final answer:
The correct adjective that can modify "les livres" is "intéressants".
Step-by-step explanation:
The correct adjective that can modify "les livres" is intéressants. In French, adjectives must agree in gender and number with the nouns they modify. Since "les livres" is plural, the adjective must also be plural. Since "livres" is masculine, the adjective should also be masculine. Therefore, the correct form is intéressants.
Learn more about Adjectives in French