Answer: The right answer is the D) Se los leo.
Explanation: Just to elaborate a little on the answer, it can be added that in this exercise they are asking you to choose the appropriate form of the personal pronoun. The sentence means "I read the books to the girls," so you must say "se los leo" (I read-them-to them). "Nos los leo" can be translated as "I read them to us" and "Me los leo" can be translated as "I read them to me." Finally, "Se lo leo" means "I read it to him/her or them." In Spanish, "se" is the reflexive form of the pronouns he, she, it, and they in accusative and dative cases, whereas "los" is the accusative form of the personal pronoun.
