What is the most commonly used structural style of folk melody?

Echoing double phrase structure up and down This is a single-paragraph music structure, and there are only two phrases in the whole song. It is the most commonly used structural style of folk melody, and it is also the basis of all the changing structures of folk melody. It is called a sentence structure, which indicates the symmetrical relationship between two phrases. This structure is consistent with the traditional aesthetic pursuit of balance and symmetry of the Chinese nation (especially the Han nationality), just like the upper and lower couplets. The melody of the previous sentence is generally on the rise, mostly falling on the fourth or fifth tone above the tonic, which naturally forms a joke; The melody of the next sentence mostly shows a downward trend of cycle and twists, and finally falls on the modal tonic, forming a perfect ending-sound. This song structure of the upper and lower sentences is widely used by folk songs in northern plateau areas such as "Xintianyou", "Qu Shan", "Climbing Mountain Tune" and "Hua 'er".