Answer:
Saber.
Explanation:
In the preterite form, "saber" takes on an irregular form. The conjugation for "saber" is shown below:
Yo- supe
Tú Supiste
Él/Ella/Usted- Supo
Nosotros/as- Supimos
Ellos/Ellas/Ustedes - Supieron
The other verbs listed do not form an irregular verb when in the preterite tense.