Rivers are on of the world's most important natural resources. Many cities are on the large rivers, and almost every country has a least one river that plays an important part in the lives of its people.
Besides transportation, rivers provide food,water for crops, water to drink, and recreation for people who live along their banks And in order to get water for crops, engineers sometimes build a dam across a river and let water become a lake behind the dam. Then people can use their water not only to irrigate fields but also to make electricity for homes and industries.
However the water often becomes polluted when cities on river bank grow in size and the number of industries increases. We are learning that it is necessary to keep rivers clean if we want to enjoy the benefits of the natural resources.
phần in đậm là đáp án