Though geologists have learned a great they still have not discovered the causes of
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Many scientists now believe that much of the heat inside the earth is produced by
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Whatever the cause of the heat may be, we do know that the earth gets hotter the further down
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The melted rock often contains steam and other gases
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Volcanic ash, cinders, and lava build up the cone-shaped mountains that we call
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【参考答案】
volcanic action.[听力原文] Geologists have been studying vo......