Final answer:
The most appropriate form of the verb to fill in the blank is 'oyeron'.
Step-by-step explanation:
The most appropriate form of the verb to fill in the blank is oyeron.
This is because 'Los niños' is a third person plural subject, so we need the third person plural form of the verb 'oír', which is 'oyeron' in the past tense.
Therefore, the correct sentence is 'Los niños oyeron música en el auditorio de la escuela ayer.'
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