Final answer:
The word 'Fuiste' is the correct word to complete the sentence. It is the second person singular form of the preterite tense of the verb 'ir' (to go) in Spanish.
Step-by-step explanation:
The correct word to complete the sentence '¿ tú al supermercado?' is 'Fuiste'.
In Spanish, the word 'Fuiste' is the second person singular form of the preterite tense of the verb 'ir', which means 'to go'.
For example, if we want to say 'Did you go to the supermarket?' in Spanish, we would say '¿Fuiste tú al supermercado?'
Learn more about Word completion in Spanish