The correct answer is C.
Desertification means the gradual transformation of arable or habitable land into desert. It is one of the world's biggest challenges today and many countries are affected by it, especially China.
Poor farming practices, increased demand for groundwater and urban development all contributed to this process.
As a result of desertification, sandstorm sweeping across northern and western China each year intensify and many people in rural areas are forced to abandon their places of living.