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What is this dialogue about

A．Teachers should set good examples.
B．Environmental pollution and protection in China.
C．People"s effort in protecting environment.
D．Government"s role in environmental protection.
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volcanic action.[听力原文]Geologists have been studying volcanoes for a long time. Though they have learned a great deal, they still have not discovered the causes of volcanic action. They know that the inside of the earth is very hot, but they thought that the heat is caused by the great pressure of the earth s outer layers. Or the heat may be left from the time when the earth was formed. During the last sixty years scientists have learned about some radioactive elements. Many scientists now believe that much of the heat inside the earth is produced by radioactive elements.Whatever the cause of the heat may be, we do know that the earth gets hotter the further down we dig. However, the pressure of the rock above keeps most materials from melting at their melting points. Geologists believe that the rock deep in the earth may be plastic, or puttylike. In other words, the rock yields slowly to pressure but is not liquid. But if some change in the earth s crust release the pressure, the rock melts. Then the hot, liquid rock can move up toward the surface.When the melted rock works its way close to the earth s crust, a volcano may be formed. The melted rock often contains steam and other gases under great pressure. If the rock above gives way, the pressure is released. Then the sudden explosion of the gases causes explosions. These blow the melted rock into pieces of different sizes and shoot them high in the air. Here they cool and harden into volcanic ash and cinders. Some of this material falls around the hole made in the earth s surface. The melted rock may keep on rising and pour out as lava. in this way, volcanic ash, cinders, and lava build up the cone-shaped mountains that we call volcanoes.
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real.[听力原文]Global warming is real. The five warmest years since good records began to be kept have all been in this decade. If you ever live through an average Chicago winter, a little bit of global warming doesn t sound bad. But one of the implications of global warming is an increase in storms. Studies have reported a 20% increase in severe storms in recent years. Another consequence of global warming is a steady melting of glaciers around the world, and that s well documented. Big chunks of the Atlantic ice cap are breaking off and floating away; every major glacier in the Northern Hemisphere is retreating; the icy summits of the Andes in south America are disappearing, an unpleasant circumstance for the farmers who rely on melt water to grow their crops. It has been suggested that all this melting ice will raise sea levels. So it will, but there s a more immediate problem. There is an awful lot of real estate now used by human beings that lies only a foot or less above sea level; a good bit of that will be flooded.Global warming is an increase in the earth s temperature due to fossil fuels, industry and agricultural processes caused by human, natural, and other gas emissions. There are many misconceptions about global warming. Some believe that pollution causes global warming, but the fact is that global warming is the result of burning fossil fuels, coal, and oil that release carbon dioxide. Another misconception is nuclear power causes climate change. Nuclear power actually reduces emissions of carbon dioxide when used in place of coal. This name is also misleading because global warming doesn t mean that it will become warmer all over, and it will actually become cold in some places.
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