Final answer:
The correct answer is 'fui'
Step-by-step explanation:
The correct answer is fui.
The verb 'ir' conjugated in the first person singular of the preterite tense is 'fui'.
In this sentence, the word 'ayer' indicates past time, so we use the preterite tense to refer to a completed action in the past.
Learn more about Spanish verb conjugation