Final answer:
The correct word to complete the sentence is 'las gemelas', which means 'twins' in English.
Step-by-step explanation:
Mónica y Blanca son las gemelas del señor Hernando.
'Gemelas' is the correct word to complete the sentence. It means 'twins' in English and refers to two people who are born at the same time to the same parents. In this case, Mónica and Blanca are twin sisters who are 14 years old.
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