The plural of library is libraries. Library, the word ends with a consonant letter plus y, so y should be changed to I plus es. The basic meaning of library is "library room", which can also refer to the library or someone's "collection of books" or "collection of recordings, records or movies". . The formula of the change law of complex number, the noun singular becomes plural, directly adding S to complement the majority, ending with S, X, Z, ch, sh, directly adding es, ending with F or fe, changing ve before adding S, adding Y, Y and I to the auxiliary suffix, and then adding es. If the suffix letter is O, three is enough. Please remember to add es, hero, tomato and potato.