The main forms of people's traditional houses in the Loess Plateau are () A, bamboo house B, igloo C, quadrangle D and cave dwelling.

People's lives are closely related to the geographical environment. In Southeast Asia, people build high-rise houses or bamboo houses to avoid high temperature and humidity and insects and snakes. The Inuit lived in the Arctic and built a strange dome "igloo" in a primitive way. Siheyuan is a traditional residential form in Beijing. After several dynasties, it finally became the most distinctive residential form in Beijing. Because of the uprightness of loess, residents on the loess plateau use local materials and dig caves. Such a house is warm in winter and cool in summer.

Therefore, choose: d.