First of all, let's say something about the noun libro. This word means book in English. Recall that a noun is a word (other than a pronoun) you use to identify people, places, or things, or to name a particular one of these called proper noun. In this way, libros is the plural form of the noun libro. It is important to say that this noun is given in masculine form and does not have a feminine form.
Is yo conozco Espana! It isn't the second or the last one because se just doesn't fit. And the third one you could technaclly say but its not the correct way.
