阅读理解。 In northern China during spring big sandstorms often make trouble for people. Sandstorms usually happen in spring. They have happened in more than 10 provinces in northern China this year. People in southern China don't have to worry about this kind of bad weather. Most of the sand comes from the north of China. In northern China, lots of places have few trees and don't get much rain. People there have been cutting down too many trees. Where there aren't many trees, the ground can't keep enough water. Over the years, the ground dries up and turns into sand. When spring comes and the ice melts, the ground becomes loose (松的), and then 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 a asthma (气喘). Sandstorms also bring farmers lots of problems. Sometimes their sheep get lost in the storms and can't get back home. The winds also tear farmer's houses down. What can you do to stop sandstorms? Here's an idea-ask your 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. 1. Sandstorms usually happen in ______ China in ______. 2. If there are ______  trees and little water in a place over the years the sandstorm will come into ______ easily. 3. Sandstorms do ______ ______  people's health, farm land and farm houses. 4. In China, sandstorms appear mainly because people ______ ______ too many trees. 5. The way to stop sandstorms is to ______ trees and ______ people from cutting down trees.