Final answer:
The correct word to complete the sentence is 'supe'. This is the first-person singular past tense form of the verb 'saber' (to know).
Step-by-step explanation:
The correct word to complete the sentence is supe.
The sentence conveys the meaning: 'I found out that the teacher had canceled the class.' In this context, 'supe' is the first-person singular past tense form of the verb 'saber' (to know).
The conjugation of 'saber' in the preterite tense is: yo supe (I knew), tú supiste (you knew), él/ella/usted supo (he/she/you(formal) knew), nosotros/nosotras supimos (we knew), ellos/ellas/ustedes supieron (they/you all knew).
Learn more about Spanish verb conjugation