Everyone tries to get to school on time. But when bad weather gives you trouble, can you still make it before the bell rings? In northern China during spring, big sandstorms often make trouble for students and everyone else. When the sky is dark with sand, buses and cars all move much more slowly. Sometimes, people can't even see for 20 metres. Sandstorms usually happen in spring. This year, sandstorms started in late March. They have happened in more than 10 provinces    in northern China this year. More than 70 million people have had problems in those places because of the sandstorms. People in southern China don't have to worry about this kind of bad weather. Most of the sand comes from Gansu and Inner Mongolia . In northern China, lots of places have few trees and don't get much rain. People there have been cutting down too many trees. When there aren't many trees, the ground can't keep enough water. Over the years, the ground dries up and turns to sand. When spring comes and the ice melts , the ground becomes looser . Strong winds take the loose sand into the sky. Sandstorms are bad for people's health. If people breathe  too much sand, they could cough or have asthma . Sandstorms also give farmers lots of problems. Sometimes their sheep get lost in the storms and never get back home. The winds also tear down farmers' houses. What can you do to stop sandstorms? Here's an idea: Ask you parents to help you plant some trees this spring. If you see people cutting down too many trees, tell them about the dangers of sandstorms, and ask your government to stop them from cutting. In which season do sandstorms usually happen?
In spring. In summer. In autumn. In winter.