【正确答案】
A
【答案解析】[听力原文] 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. They contain important eco-systems, 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. 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, eco-systems' supporting plants and animals 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. Many activities including research and development projects have been planned for next year. The UN Food and Agriculture Organization is leading this special recognition of mountains. Why are mountains a very important part of the earth's ecology and environment? 关于山脉是地球生态和环境重要组成部分的原因，短文中提到，山脉包含了重要的生态体系，比如说森林。它们还为地球上约十分之一的人口提供最为重要的资源，并为地球上超过半数的人提供商品和服务，故选A。