Final answer:
The word that completes the sentence is 'aburre'.
Step-by-step explanation:
The word that correctly completes the sentence is aburre. In this sentence, the subject 'la escuela' (the school) is singular, so we use the singular form of the verb 'to bore', which is 'aburre'. If the subject was plural, we would use the plural form 'aburren'.
Learn more about Choosing the correct form of the verb 'to bore' in Spanish