Final answer:
The subject pronoun that best completes the sentence 'tenemos que comprar los útiles' is nosotros.
Step-by-step explanation:
The subject pronoun that best completes the sentence 'tenemos que comprar los útiles' is nosotros.
In this sentence, 'tenemos' is conjugated for the pronoun 'nosotros', which means 'we' in Spanish. So, the correct answer is (D) Nosotros.
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