Answer: Se venden libros en la librería.
Explanation: Completing the sentence with the correct form of the verb in parentheses using an impersonal construction with se is Se venden libros en la librería. This is a Spanish impersonal construction. It is used to express the impersonal subjects one, you, they and people. It is often used to state what people do. The verb is always in the third person either singular or plural.
