阅读理解。

     Rivers are one of our most important natural resources (自然资源). Many of the world's great cities

are located on rivers, and almost every country has at least one river flowing 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. 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, and chances for fun and

recreation for the people who live along their banks. In order to increase 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 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.

1. The greatest river for navigation is _______.

A. the Amazon

B. the Nile

C. the Mekong

D. the Mississippi

2. Which is wrong? 

A. The Nile is in India.

B. Almost every country has at least one important river.

C. Many cities are located on rivers.

D. Rivers play an important part in the lives of people.

3. 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

4. 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

5. The best title of the passage is _______.

A. Rivers in Cities

B. The importance of Rivers

C. Transportation

D. Natural Resources