Because the first part is three or four tones. Generally, the method of leveling is used to distinguish upper and lower couplets. The last word of the couplet is flat and parallel (the third and fourth tones), and the last word of the couplet is flat and parallel (the first and second tones), that is, the last word of the couplet is flat and parallel.
Couplets, also known as antithesis, door-to-door, spring stickers, Spring Festival couplets, couplets and so on. It is a antithesis written on paper, cloth or carved on bamboo, wood and columns. The antithesis of couplets is neat and even, which is a unique artistic form of Chinese. Couplets are the treasures of China traditional culture.