Final answer:
The best word to complete the sentence is 'esas'
Step-by-step explanation:
The word that best completes the sentence is esas.
This is because the sentence is referring to specific mountains that are visible in the distance, so the demonstrative pronoun used should be 'those' or 'esas' in Spanish.
For example: 'Las montañas que ves allá en la distancia (a lo lejos) son más altas que esas.' (The mountains you see over there in the distance are taller than those.)
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