Rivers are one of our most important natural resources (资源). Many of the world's great cities are located(坐落) on rivers, and almost every country has at least one river running through it that plays an important role in the lives of its people.
Since the beginning of the history, people have used rivers for transportation(运输). The longest one in the United States is the Mississippi. The lifeline of Egypt is the Nile. To the people of India, the Gangs is great, but it is also important for transportation; Ships can travel along it for a thousand miles. Other great rivers are the Congo in Africa and the Mekong in southeast Asia. The greatest of all for navigation (航海), however, is the Amazon in Brazil. It is so wide and so deep that large ships can go about two thousand miles upon it.
Besides transportation, rivers give food, water to drink, water for crops(庄稼), and chances for fun and entertainment for the people who live along their banks. In order to increase(增加) the supply of crops, engineers sometimes build a dam (大坝) across a river and let a lake from behind the dam. Then people can use the water not only to irrigate (灌溉) their fields but also to make electricity for their homes and industries.
However, large cities and industries that are located upon rivers often make problems. As the cities grow in size and industries increase in number, the water in the rivers becomes polluted with chemicals(化学物质) and other materials. People are learning the importance, however, of doing more to keep their rivers clean if they want to enjoy the benefits (利益) of this natural resource.
小题1:The greatest river for navigation is ___________.
A．the Amazon
B．the Nile
C．the Mekong
D．the Mississippi小题2:From a dam, people can use the water for ___________.
A．keeping the rivers clean
B．only making electricity
C．washing clothes
D．irrigation and making electricity小题3:The water in the river is polluted because of _____________.
A．people's drinking water too much
B．people's swimming in the river too much
C．chemicals and other materials
D．people's building a dam across a river小题4:The best title of the passage is ___________.
A．Rivers in Cities
B．The importance of Rivers
C．Transportation
D．Natural Resources
小题1:A
小题2:D
小题3:C
小题4:B
题目分析：短文大意：本文主要讲述了河流对于人类生活的重要性，以及河流收到污染的事实。
小题1:细节理解题。根据短文第二段The greatest of all for navigation (航海), however, is the Amazon in Brazil.描述，可知世界上最好的用来航行的河流是亚马逊河。故选A。
小题2:细节理解题。根据短文倒数第二段In order to increase(增加) the supply of crops, engineers sometimes build a dam (大坝) across a river and let a lake from behind the dam. Then people can use the water not only to irrigate (灌溉) their fields but also to make electricity for their homes and industries.描述，可知在河流中建好大坝后，人们不仅可以用喝水来灌溉，还可以利用河水来发电。故选D。
小题3:细节理解题。根据s the cities grow in size and industries increase in number, the water in the rivers becomes polluted with chemicals(化学物质) and other materials. 描述，可知喝水由于化学物质和其它东西收到了污染。故选C。
小题4:标题归纳题。阅读短文可知本文主要讲述了河流对于人类生活的重要性，以及河流收到污染的事实。故选B，河流的重要性。