Final answer:
The correct form of the irregular verb in the preterite tense that best completes the sentence is "hicimos".
Step-by-step explanation:
The correct form of the irregular verb in the preterite tense that best completes the sentence "Nosotros ________ ejercicio cada mañana." is "hicimos". In the preterite tense, the verb "hacer" (to do/make) conjugates irregularly for the first person plural (nosotros) form. The conjugation for "hacer" in the preterite tense for nosotros is "hicimos".
Learn more about Spanish verb conjugation