Final answer:
The verb form 'gastamos' is the correct choice to complete the sentence.
Step-by-step explanation:
The correct verb form to complete the sentence is gastamos.
The sentence is referring to an action that Ana and the student did yesterday using the first person plural (yo) form of the verb. In Spanish, the verb 'gastar' means 'to spend', and the correct conjugation for the past tense is 'gastamos'.
Therefore, the correct sentence is 'Ayer, Ana y yo gastamos 20 000 pesos para comprar ropa.' meaning 'Yesterday, Ana and I spent 20,000 pesos to buy clothes.'
Learn more about Spanish verb conjugation