El auto es hermanas.
a. a lasc. a losb. de lasd. de los

El auto es B. de las hermanas.

Explanation: The option that fills in the blank is "de las" because the sentence makes reference to a car that belongs to some sisters. In that way, as it is referring to a belonging, the preposition that must be used is "de" and not "a". Moreover, as the noun that comes after the possessive is feminine ("hermanas"), the article must also be feminine ("las"). In that way, the correct option is "de las".