Ayer leí un libro en la biblioteca. This means in English: I read a book in the library yesterday. Helado means ice-cream in English, so it lacks sense in the context of the sentence. Bibliotecario means librarian, which also is incoherent since you cannot read a person. Revista is magazine, which would make sense but it's a female noun, and the word "un" indicates that the noun should be masculine. So the only possible option is libro.
