The traditional folk houses located in the south of China are () A, Bamboo House B, Cave C, Mongolian yurt D, four in one.

Many traditional residential buildings in China often adapt to the local natural environment. Most areas in the south belong to subtropical monsoon climate, with high temperature and abundant precipitation in summer, and the roof slope of houses is large, which is convenient for drainage. Most people live in bamboo buildings (diaojiao buildings), which are both heat-insulating and convenient for rainwater drainage. So option d fits the question.

Therefore, choose: d.