1 . After years of heated debate, gray wolves were reintroduced to Yellowstone National Park. Fourteen wolves were caught in Canada and transported to the park. By last year, the Yellowstone wolf population had grown to more than 170 wolves.

Gray wolves once were seen here and there in the Yellowstone area and much of the continental United States, but they were gradually displaced by human development. By the 1920s, wolves had practically disappeared from the Yellowstone area. They went farther north into the deep forests of Canada, where there were fewer humans around.

The disappearance of the wolves had many unexpected results. Deer and elk populations — major food sources (来源) for the wolf — grew rapidly. These animals consumed large amounts of vegetation (植被), which reduced plant diversity in the park. In the absence of wolves, coyote populations also grew quickly. The coyotes killed a large percentage of the park’s red foxes, and completely drove away the park’s beavers.

As early as 1966, biologists asked the government to consider reintroducing wolves to Yellowstone Park. They hoped that wolves would be able to control the elk and coyote problems. Many farmers opposed the plan because they feared that wolves would kill their farm animals or pets.

The government spent nearly 30 years coming up with a plan to reintroduce the wolvers. The U.S. Fish and Wildlife Service carefully monitors and manages the wolf packs in Yellowstone. Today, the debate continues over how well the gray wolf is fitting in at Yellowstone. Elk, deer, and coyote populations are down, while beavers and red foxes have made a comeback. The Yellowstone wolf project has been a valuable experiment to help biologists decide whether to reintroduce wolves to other parts of the country as well.

2 . Using too much water or throwing rubbish into our rivers are clear ways that humans can put our water supply in danger, but we also affect our water supply in less obvious ways. You may wonder how paving(铺砌) a road can lead to less usable fresh water. A major part of the water we use every day is groundwater. Groundwater does not come from lakes or rivers. It comes from underground. The more roads and parking lots we pave, the less water can flow into the ground to become groundwater.

Human activity is not responsible for all water shortages(缺乏). Drier climates are of course more likely to have droughts(干旱) than areas with more rainfall, but in any case, good management can help to make sure there is enough water to meet our basic needs .

Thinking about the way we use water every day can make a big difference, too. In the United States, a family of four can use 1.5 tons of water a day! This shows how much we depend on water to live, but there’s a lot we can do to lower the number.

You can take steps to save water in your home. To start with, use the same glass for your drinking water all day. Wash it only once a day. Run your dishwasher only when it is full. Help your parents fix any leaks(滴水) in your home. You can even help to keep our water supply clean by recycling batteries instead of throwing them away.

5 . Think about the different ways that people use the wind. You can use it to fly a kite or to sai1a boat. Wind is one of our of our cleanest and riches power source(来源) ,as well as one of the oldest . Evidence shows that windmills(风车) began to be used in ancient Iran back in the seventh century BC .They were first introduced to Europe during the 1100s,when armies returned from the Middle East with knowledge of using wind power .

For many centuries ,people used windmills to grind(磨碎)wheat into flour or pump water from deep underground when electricity was discovered in the 1ate 1800s,people living in remote areas began to use them to produce electricity. This al1owed them to people in almost all1 areas of the United States, windmills were rarely used. During the course 1970s, people started becoming concerned about the pollution that is created when coal and gas are burned to produce electricity. People also realized that the supply of coal and gas would not last forever. Then, wind was rediscovered, though it means higher coasts. Today, there is a global movement to supply more and more of our electricity through the use of wind .

10 . To take the apple as a forbidden fruit is the most unlikely story the Christians ever cooked up. For them, the forbidden fruit from Eden is evil(邪恶的). So when Columbus brought the tomato back from South America, a land mistakenly considered to be Eden, everyone jumped to the obvious conclusion. Wrongly taken as the apple of Eden, the tomato was shut out of the door of Europeans.

What made it particularly terrifying was its similarity to the mandrake, a plant that was thought to have come from Hell(地狱 ) What earned the plant its awful reputation was its roots which looked like a dried-up human body occupied by evil spirits. Though the tomato and the mandrake were quite different except that both had bright red or yellow fruit, the general population considered them one and the same, too terrible to touch.

Cautious Europeans long ignored the tomato, and until the early 1700s most of the Western people continued to drag their feet. In the 1880s, the daughter of a well-known farmer wrote that the most interesting part of an afternoon tea at her father's house had been the "introduction of this wonderful new fruit--or is it a vegetable? ""As late as the twentieth century some writers still classed tomatoes with mandrakes as an "evil fruit".

But in the end tomatoes carried the day. The hero of the tomato was an American named Robert Johnson, and when he was publicly going to eat the tomato in 1820, people journeyed for hundreds of miles to watch him drop dead. "What are you afraid of? "he shouted. "T"ll show you fools that these things - are good to eat! Then he bit into the tomato, Some people fainted. But he survived and, according to a local story, set up a tomato-canning factory.