Final answer:
The correct word to complete the question is 'estas'.
Step-by-step explanation:
The correct word to complete the question is estas. The question is asking 'Do you want to buy a trumpet or that one?'. In Spanish, the demonstrative pronoun 'aquella' refers to something far from both the speaker and the listener. Since 'aquella' is feminine singular, we need to use the feminine plural form 'estas' to match it. The correct question would be '¿Quieres comprar trompeta o estas?'
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