Final answer:
In the preterite tense, the verb 'tener' changes to 'tuvo' for the third person singular, hence the sentence should read 'Maria tuvo una fiesta el sábado pasado.'
Step-by-step explanation:
The correct form of the irregular verb in the preterite tense for the sentence 'Maria _____ (tener) una fiesta el sábado pasado' is 'tuvo'. Therefore, the sentence should be completed as 'Maria tuvo una fiesta el sábado pasado.'
The preterite tense is used to describe actions that were completed in the past, and the verb 'tener' is an irregular verb in the preterite tense. In the case of the verb 'tener' from the "UV" family of irregular verbs, the preterite form does not follow the regular patterns. Instead, its preterite form changes to 'tuvo' for the third person singular, which matches the subject 'Maria'.