阅读理解。 Plants and animals, including humans, need food and water to live on. These are from the  natural resources(资源) on Earth. To protect these resources, we need to keep the air clean and the water drinkable. We need to keep the soil (土壤)healthy. How do we do that? Protect the land The soil that covers fields and farms provides much of the food we eat. Human activities  such  as plowing(耕) fields, mining(采矿), and building highways can destroy (破坏)the land. Erosion happen when wind and water carry away the soil. Soil erosion can turn rich farmland into a desert  wasteland. So does this mean we shouldn't build a highway or plow a field? Of course not. But  it does mean  we might think about Earth-friendly ways of doing those things. Today farmers plow their fields in different ways to pr erosion. They try to use less water for their crops. They keep animals from eating the growing grass in  just one  area. Farmers also plant  trees  to pr erosion from happening. Save the Trees Another human activity that damages the land is deforestation(采伐森林). People take away a large number of trees from a forest. Millions of square kilometers of forest disappear each year. When  this happens, many plants and animals lose their  places to live. They may die  out, or  become  very  few. Scientists haven't even discovered all the living things in the forest. We may be losing some without even knowing they are there. Trees absorb (吸收)and use carbon dioxide (二氧化碳)when they make food. Environmentalists encourage careful management of the forests. They ask people to replant trees  after they cut down the forest. Recycle, Reuse, Reduce People throw a piece of paper into the wastebasket after using it. The paper becomes trash.  Where does the trash go next? Much of our trash ends up in landfills(垃圾填埋地). They take up valuable land and sometimes pollute the water, air, and land around them. More than a third of the  trash in  landfills  is paper. Recycling, reusing, and reducing what you throw away can cut down on the need for more landfills. In fact, we can recycle about eighty percent of household trash. 1. What does the underlined word erosion mean? A. Plowing fields and mining B. Cutting down trees and farming. C. Wind and rain carrying away soil. D. Building highways on the farmland. 2. Why do we need to save the trees? A. To discover more new trees every year. B. To encourage careful management of the forest. C. To take away a large number of trees from the forest. D. To keep good places for animals and plants to live in. 3. How much of the trash can we recycle? A. All the trash. B. Very little. C. One third. D. Four fifths. 4. What's the purpose of the author writing the passage? A. To ask people to look for places to plant trees. B. To tell people how to protect natural resources. C. To show how the lands are destroyed by people. D. To discuss ways of protecting animals and plants.