Rivers are one of our most important naturalresources(资源). Many of the world’s great cities are located on rivers, and almost every country has at l______one river running through it that plays an important part in the lives of its people.

Since the beginning of history, people have used rivers for transportation. The longest one in the United States is the Mississippi. The lifeline of Egypt is the Nile. To the people of India, the Ganges is great, but it is also important for transportation; ships cant______along it for a thousand miles. Other great rivers are the Congo in Africa and the Mekong in southeastern Asia. The greatest of all fornavigation（航海）, however, is the Amazon in Brazil（巴西）. It is so wide and so deep that large ships can go about two thousand miles up it.

B_______transportation, rivers give food to eat, water to drink, water for crops, and chances for fun. In order to increase thesupply(供给) of water for crops, engineers sometimes build adam(大坝) a________a river and let a lake form behind the dam. Then people can use the water not only toirrigate(灌溉) their fields but also top_______electricity for their homes and industries.

However, large cities and industries that are located on rivers often cause problems. As the cities grow in size and industries increase in number, the water in the rivers becomes polluted with c_______and other materials. People are learning the importance, however, of doing more to keep their rivers clean if they want to enjoy thebenefits(利益) of these natural resources.

【小题1】l___________
【小题2】t_____________
【小题3】B_____________
【小题4】a__________
【小题5】p____________
【小题6】c______________