Tatiana, ¿conoces a las hermanas de Andrés?
Tatiana: Sí, yo _____ conozco.
Answer: D) Tatiana: Sí, yo las conozco.
Tatiana, do you know Andres's sisters?
Tatiana: Yes, I know them.
Step-by-step explanation: The direct object of the verb "conocer" is "las hermanas". The direct object pronoun must agree in gender and number. Feminine, plural, "las"