Final answer:
The correct verb form to complete the sentence is 'supe' as the subject 'yo' indicates the first-person singular form.
Step-by-step explanation:
The correct verb form to complete the sentence is supe.
Since the subject 'yo' (I) indicates the first-person singular form, the appropriate verb form in the past tense is 'supe'. The verb 'saber' conjugated in the first-person singular preterite tense becomes 'supe'.
For example, 'ayer yo supe que empezaste a trabajar' translates to 'Yesterday, I knew that you started working'.
Learn more about Spanish verb conjugation