Dragon Leaping Tianmen and Tiger Crouching at Phoenix Tower should be duals, because the characteristics of the dual sentences are neat antithesis, lively rhythm, neat and beautiful, easy to memorize, the number of words, structure and part of speech are the same, and these two words are four. There are two characters, and there are dragons and phoenixes, and the verbs in them are also corresponding. Therefore, these two words should be said to be dual.