Final answer:
The word that best completes the sentence is 'guapas'.
Step-by-step explanation:
In the given sentence, the word that best completes the sentence is guapas. The subject of the sentence, Olivia y Lola, is plural and feminine. In Spanish, adjectives must agree in gender and number with the noun they modify. Since Olivia y Lola is plural and feminine, the adjective guapas (meaning beautiful) agrees with this by also being plural and feminine.
Learn more about Gender and number agreement in Spanish