<h3>El bibliotecario: Buenas tardes, ¿en qué puedo ayudarla?</h3><h3>Carolina: Estoy buscando __ libro que tenga poemas de amor.</h3>
Answer: A. un) Estoy buscando un libro que tenga poemas de amor.
Translation: I'm looking for a book that has love poems.
Explanation: The direct object in this sentence is "libro", which is a singular masculine noun, so the article that accompanies it has to agree with the noun. In addition he does not specify the book so the indefinite article is used. Un libro.