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As viewed from space, the Earth’s distinguishing characteristics are its blue waters and white clouds. Enveloped by an ocean of air consisting of 78% nitrogen and 21% oxygen, the planet is the only one in our solar system known to harbor life. Circling the Sun at an average distance of 149 million km (93 million miles), the Earth is the third planet from the Sun and the fifth largest planet in the solar system. Its rapid and molten nickel-iron core give rise to an extensive magnetic field which, coupled with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Most meteors burn up in the Earth’s atmosphere before they can strike the surface. The planet’s active geological processes have left no evidence of the ancient pelting it almost certainly received soon after it was formed. The Earth has a s A. Humans have built over most of the craters. B. Most meteors fell into the ocean and not on land. C. The Earth’s magnetic field repelled most meteors. D. The Earth’s natural geologic activity has eliminated most traces. [单项选择]Happy Earth Day
The Good News Here’s the good news: our air is cleaner, our lakes are purer, our forests are healthier, endangered species are recovering, toxic emissions are down, and acid rain has diminished dramatically. And yet, if you’ve looked at a newspaper or watched the evening news lately, you might think our environment is under siege (围攻). Media Coverage of the environment is heavy on doomsday, but the truth is not at all bleak: nearly all environmental trends in the United States are positive and have been for years—if not decades. Eco-legislation, green organizations, corporate cooperation and new inventions have all quietly steered our environment in a positive direction. We can’t afford to be complacent (自满的), though—especially when it comes to greenhouse gases, since global warming is the one huge problem we haven’t really tackled. But almost every measure taken by government agencies and grass-roots efforts to improve the environment has A. The Potomac River B. Boston Harbor C. The Chicago River D. The Mississippi River 我来回答: 提交
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