Answer: las herramientas
Sentence: El mecánico usa las herramientas y nos dice que son sus favoritas.
Translation: The mechanic uses the tools and tells us that they are his favorites.
Step-by-step explanation:
Since the direct object pronoun is "las", which is feminine and plural and must agree with the direct object in gender and number, the direct object must also be a feminine and polural noun. The only feminine and plural noun option is "las herramientas".
Spymore