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  3. Trillions of incredibly tiny diamonds, possibly formed by a dying star before the solar system was born 4.5 billion years ago, h

Trillions of incredibly tiny diamonds, possibly formed by a dying star before the solar system was born 4.5 billion years ago, h

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问题      Trillions of incredibly tiny diamonds, possibly formed by a dying star before the solar system was born 4.5 billion years ago, have been found by researchers 【C1】______ four meteorites.
     The powder-like diamonds could be among the oldest things in the 【C2】______ , said Roy Lewis, senior research associate at the University of Chicago.
      The diamonds may 【C3】______ clues about the chemistry of stars, and if scientists can determine how they formed, that could suggest better ways of manufacturing tiny diamonds for 【C4】______ purposes, he said.
     "It’s quite possible that nature is doing it more 【C5】______ than we’ve been doing it," he said. "So maybe we’ve got something to learn."
     The new find is 【C6】______ , said John Wood, staff scientist at the Harvard-Smithsonian Centre for Astrophysics. Although diamonds have been found before in meteorites, they were formed relatively recently 【C7】______ the shock of impact, he said in a telephone interview.
     But Wood said the new report made him "quite sure" the newly found diamonds are older than the sun.
     Lewis said researchers never expected to find diamonds when they started 【C8】______ a stone-like meteorite that had plunged into Mexican cornfield in 1969.
     They were studying an unusual carbon dust in the meteorite, and to purify the sample they went though several steps to dissolve other materials. They expected the sample to remain black through the purification, but to their surprise in the final step it turned 【C9】______ .
     Lewis said they believed the final stage had dissolved the carbon they wanted to study. But tests showed that the white residue was in fact made of carbon. Other tests found that it contained an unusual combination of forms of the gas xenon, 【C10】______ that it came from outside the solar system.
     Still another battery of tests 【C11】______ the residue as diamond dust, so fine that a row of 20,000 grains would extend about the 【C12】______ of a human hair.
     The researchers also found diamonds in three other meteorites, Lewis said. Tests showed all four meteorites were as old as the solar system, and that the embedded diamonds did not form within the meteorite 【C13】______ of collisions.
     So the diamonds must have 【C14】______ somewhere else before the meteorites formed, making them as old or older than the solar system.
     The diamonds may have formed in the upper atmosphere of a star in the late "red giant" stage, where the temperature and abundance of hydrogen could 【C15】______ diamonds to form as carbon gas condenses.  
【C14】
选项 A、risen
B、disappeared
C、arisen
D、encountered
答案C
解析 arise“出现”，该句意为“早在陨石形成之前，金刚石就应该已经形成了”。
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