slang
slang统指俚语，并不指一个一个的俚语，前面不可加a，也没有复数形式slangs。如可以说This word is slang和All these phrases are slang，不可说This word is a slang和All these phrases are slangs.
但 a slang可以指“一种俚语”，slangs可以指“多种俚语”。例如：They have a slang of their own. 和I do not know a single expression of military and naval slangs.
