Final answer:
To rewrite the sentence in the passé composé, use the verb 'sortir' and conjugate it according to the subject.
Step-by-step explanation:
To rewrite the sentence l'école à trois heures in the passé composé, you need to use the auxiliary verb avoir followed by the past participle of the main verb.
The verb sortir (to go out) conjugated in the passé composé for the subject nous is nous sommes sortis.
Therefore, the rewritten sentence in the passé composé would be Nous sommes sortis de l'école à trois heures.
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