Final answer:
The correct conjugation is 'puedes'.
Step-by-step explanation:
The correct conjugation is puedes. The sentence '¿Qué comprar con quinientos pesos?' is asking 'What can you buy with five hundred pesos?' In this context, the subject 'tú' ('you') is implied, and the correct conjugation of the verb 'poder' ('to be able to') should be in the second person singular form, which is 'puedes'.
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