A、They contain important ecosystems. B、They provide the most important resources for one-fifth of the world’s population. C、They

Mountains are about one-fifth of the world’s land surface area. Mountains are a very important part of the earth’s ecology and environment.[26]They contain important ecosystems, such as forests. They provide the most important resources for about one-tenth of the world’s population. Mountains also provide goods and services to more than half the people in the world.
    Melting snow from mountains provides water for hundreds of millions of people.[27]For example, the Himalayan Mountains supply drinking water for the people of India. Mountains are also important areas for winter sports. Millions of people visit countries in Europe to ski down mountains every year.
    Mountains are important to the world. But there are problems involving mountains in many places. People who live in mountain areas are usually poor. There is often very little economic activity in these areas. Mountain environments are sometimes not supervised very well. When this happens, ecosystems supporting plant and animal life suffer.
    In some areas, too many trees are cut down. When it rains heavily, water can rush down the sides of mountains and flood villages and cities. Serious flooding kills many people and animals every year. In addition, earthquakes can cause hillsides to come crashing down in powerful landslides.
    The United Nations wants to help more people learn about the importance of mountains as well as their problems. So the UN General Assembly has named the year 2002 the International Year of Mountains.
26. In what way are mountains important to the world?
27. For whom does the Himalayan Mountains supply drinking water?
28. Why has the United Nations named the year 2002 the International Year of Mountains?