单选题 1
summary of the physical and chemical
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of life must begin, not on the Earth, but
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the Sun; in fact,
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the Sun"s very center.
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is here that is to be found the
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of the energy that the Sun constantly
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space
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light and heat. This energy is liberated at the center of the Sun as billions upon billions of nuclei hydrogen atoms
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each other and
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to form nuclei of helium, and,
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doing so,
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some of the energy that is stored in the nuclei of atoms. The output of light and heat of the Sun
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that some 600 million tons of hydrogen
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helium in the Sun every second. This the Sun
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for several thousands of millions of years.