Final answer:
The best Spanish word to complete the sentence is "somos" which means "we are".
Step-by-step explanation:
The best Spanish word to complete the sentence "Nosotros __________ de las montañas" is "somos". This word means "we are" in English. So the complete sentence would be "Nosotros somos de las montañas" which translates to "We are from the mountains".
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