Why did Zhangye, Gansu Province encounter a rare sandstorm? 20 18 this year

It can be seen from the materials that the natural causes of sandstorms in China are land desertification, less precipitation in spring and more cold waves and windy weather in winter and spring; Man-made reasons are serious vegetation destruction, and sand sources are brought by construction sites and uncultivated land. Measures to control sandstorms include planting more trees and grass in Inner Mongolia and returning farmland to forests and grasslands.

So choose: C.