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  3. Seven of America’s Natural Wonders Niagara Falls The United States shares Niagara Falls with Canada. That thundering crash i

Seven of America’s Natural Wonders Niagara Falls The United States shares Niagara Falls with Canada. That thundering crash i

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问题                     Seven of America’s Natural Wonders
Niagara Falls
    The United States shares Niagara Falls with Canada. That thundering crash is the tens of thousands of cubic feet of water that flow each second over Niagara Falls which includes the American Falls and Horse- shoe Falls. The American Falls in New York State extends more than 320 meters across part of the Niagara River. The American Falls is more than 50 meters high.
    Canada owns the larger Horseshoe Falls. It is about 800 meters wide and almost 50 meters high. It is shaped like the letter U, or a horse’s shoe.
    Niagara Falls formed about 12,000 years ago when huge melting sheets of ice formed the Great Lakes. The land was uneven with several drops in level, some very sharp. Water from Lake Erie began to flow north to Lake Ontario as a result of the loss of the ice barrier.
The Everglades(大沼泽)
    The Everglades once called "the liquid heart" lies in the state of Florida.
    Hundreds of birds fly in a sunny blue sky. The only sounds are bird calls and the soft noise made by tall grasses as the water slowly moves them. Hidden in the grasses, dark green alligators(美洲鳄)move at the edge of the water, like part of the Earth come alive.
    This is the Everglades -- a low, watery, partly coastal area that covers 10,000 square kilometers. The area is filled with sawgrass. This plant grows in sharp, thin pieces that are 3 to 10 meters tall. The Everglades is sometimes called "river of grass."
    The area also contains forests of palm, cypress(柏树), mangrove(红树林)and pine. And beautiful plants and sweet-smelling flowers grow in the Everglades. These include several kinds of the highly prized and rare flower, the orchid(兰花). Animal species are plentiful. Many colorful birds and butterflies live here. So do snakes, foxes, frogs and even big cats, called Florida panthers(黑豹). But, the Everglades alligators and crocodiles are probably the animals most identified with the Everglades. No other place in the world is home to both.
Badlands
    In the state of South Dakota, the land is big and mostly flat with many fields of corn, wheat and soy-beans. But as the tourists traveling west, the cropland gives way to wild grasses. A strong dry wind blows continuously from the west.
    Suddenly, the land becomes torn and rocky, dry and dusty -- no longer green and gold. It is now a light red-brown color. All around are broken disordered forms. There are hills and valleys of all sizes and strange shapes.
    These are the Badlands. Hundreds of thousands of years ago the area was grassland. But, then, forces of nature destroyed the grass. Water and ice cut into the surface of the earth. They beat at the rocks, wearing them away. The result is one of the world’s strangest sights.
    All together, the Badlands cover more than 15,000 square kilometers. About 10 percent is national parkland. The area is a study in extremes. Temperatures in the summer have been as high as 46 degrees Celsius. In the winter they have dropped to as low as 41 degrees below zero. Life in the Badlands is difficult. But animals do survive. The most well known is the prairie dog. This small mammal lives in a series of underground passages.
The Grand Canyon
    The Grand Canyon is a huge hole in the Earth in the state of Arizona. The first sight is breathtaking. The Grand Canyon stretches for hundreds of kilometers before us and hundreds of meters below us. It is about 24 kilometers across at its widest point. Its deepest point is almost 2,000 meters down.
    The Grand Canyon is a series of deep long cuts in rock. There are many passages and large raised areas. There are forests on the top level and desert areas down below. They provide support for several different ecosystems. The Colorado River flows through the Grand Canyon. The Canyon offers a lot of information about the physical history of Earth. There is a huge amount of fossil evidence. And its walls provide a record of 3 of the 4 major periods of the Earth’s geologic time.
Death Valley
    The hottest, driest and lowest place in North America is Death Valley. Death Valley is part of the Mojave Desert(莫哈韦沙漠). It lies mostly in the western state of California although part of it reaches into Nevada.
    An area called Badwater sits about 86 meters below sea level. There is not really any water there. The area gets fewer than 5 centimeters of rain a year.
    During the summer the temperature in Death Valley can reach 57 degrees Celsius. But, it can be dangerously cold in the winter there, too. And storms in the mountains can produce sudden flooding on the valley floor.
    In other words, Death Valley is an unforgiving place. The heat has killed people in the past. And it will continue to kill those who are not careful in dealing with the area’s extreme climate.
    Death Valley holds much evidence of nature’s past violence. For example, there is Ubehebe Crater(火山爆发后的弹坑). This hole is about 1 kilometer across and more than 230 meters deep. It is the remains of a major volcanic explosion about 200 years ago.
The Glaciers in Alaska
    We could probably just call all of Alaska a natural wonder. But, of special interest are its glaciers. These huge, slow-moving masses of ice cover about 75 thousand square kilometers.
    About 100,000 of these rivers of ice flow down mountains. Some start from thousands of meters up a mountain. They can flow to areas just a few hundred meters above sea level. The largest Alaskan glacier is called Malaspina. It is more than 2,200 square kilometers.
    Most glaciers move very slowly. But sometimes one will suddenly speed ahead for a year or two. These are called surge-glaciers(汹涌的冰川). The most recent surges were in 2000. The Tokositna Glacier and Yanert Glaciers now have deep, narrow cuts on their formerly smooth surfaces. Yanert Glacier dropped 91 meters as a result of the surge. It is always very cold on the glaciers.
Mount Kilauea
    Mount Kilauea is the world’s most active volcano. It is on the island of Hawaii. Kilauea is not far from Mauna Loa, the largest volcano in the world.
    Kilauea has been releasing burning hot liquid rock called lava(熔岩)continuously since 1983. The lava flows down the mountain to the Pacific Ocean. Its fierce heat produces a big cloud of steam when it hits the cold water. Kilauean lava continues to add land to the island. Sometimes visitors are able to walk out near the edge of this new black volcanic rock.
Alaska is a natural wonder, about  thousand square kilometers are covered by glaciers, which are huge, slow-moving ______.
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答案masses of ice
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