U1E3 Irregular preterite verb

IR verbs that change stems in the present tense also change stems in the preterite tense. The endings are regular preterite tense endings, but in the él, ella, Ud. and ellos, ellas, Uds. forms the stem changes.
we have also learned that leer, creer and oír are irregular in the 3rd person singular and plural in the preterite.