Which Spanish direct object pronoun would you use in place of "el libro"?

lo

Translation: it

Explanation:

Direct object pronouns in Spanish change gender and number depending on the noun or nouns they replace.  

Since "el libro" is a masculine and singular noun, the direct object pronoun that replaces it must also be masculine and singular: Lo

Example:

Spanish: He leído el libro. Lo he leído.

Translation: I have read the book. I have read it.

alright, that is a bet.