Traditional Tibetan farm tools

Niu Geng appeared in the late Spring and Autumn Period; After the mid-Western Han Dynasty, Niu Geng was widely popularized. When the plow wall is used, it can complete the processes of turning over soil, stubble cleaning, ditching and ridging at the same time. Since the plough wall was used, Niu Geng has been widely popularized. So rule out a, b and d.