C

    Rivers are one of our most important natural resources(资源). Many of the world's great cities are located on rivers, and almost every country has at least one river 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 can travel along it for a thousand miles. Other great rivers are the Congo in Africa and the Mekong in southeastern 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 up 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 water for crops, engineers sometimes build a dam(坝) across a river and let a lake form 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 on rivers often cause problems. As the cities grow in size and industries increase, 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 of them.

任务型阅读

    Every time we get behind the wheel of a car, we put our lives and the lives of others at risk. Self-driving cars are designed to reduce those risks by letting technology control our vehicles.

    Accident rates for self-driving cars have been much lower than the rate, for human-driven cars. ____

    As humans, we can make moral choices in avoiding accidents. To avoid hitting a child, for example, human drivers might sharply turn a car away from the child even if others may be injured. ____ Researchers studied this issue. They have developed the Moral Machine website to help explore the choices self-driving cars should make.

    ____ You are shown two possible traffic situations and you choose between them. An accident will take place. You choose how many living beings would be hurt or killed.

    In one situation there may be a female doctor, a child, two dogs and a homeless person who would be killed. In the other situation, you might have two babies and a cat who would be killed. ____

    The Moral Machine website has many situations and many possible outcomes. When you click on the situation of your choice, it will be highlighted. ____ At the end of the situation, you are shown the results, based on the choices you made. The results show which character you were most likely to save and which character you were most likely to have die.