2. 外语
  3. Sparks created in a lab give off X-rays, scientists announced Monday. X-rays are a byproduct(副产物) of high-energy electron di

Sparks created in a lab give off X-rays, scientists announced Monday. X-rays are a byproduct(副产物) of high-energy electron di

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问题     Sparks created in a lab give off X-rays, scientists announced Monday.
    X-rays are a byproduct(副产物) of high-energy electron discharges in the Sun, in exploding stars, and even in lightning. Many scientists did not expect sparks alone to do the trick.
    Researchers at Florida Institute of Technology brought their equipment, which had detected X-rays in lightning, into the lab. Half the team expected to see X-rays and the other half did not.
    In sparks of 1.5 million to 2 million volts, the researchers indeed recorded X-rays that were remarkably similar to those produced by lightning.
    "This amazed us, It opens the door to answering really big questions about lightning by generating it in the lab," said team member Hamid Rassoul. "It also tells us that we have a lot’to learn about how even small sparks work."
    X-rays are a form of electromagnetic radiation, on a spectrum(频谱) that runs from radio waves on the low end to gamma rays on the high end and includes visible light, too.
    Scientists don’t know why lightning spawns X-rays. They theorize it involves a "runaway breakdown" of the air, in which electrons escape their normal connections and gain very large energies.
    "We didn’t think X-rays could be made so easily in the air," said study leader Joseph Dwyer. "The results should allow for the detailed laboratory study of runaway breakdown, a mechanism that may play a role in thunderstorm electrification, lightning initiation and propagation, and terrestrial(地球的) gamma-ray flashes."
选项 A、making sparks in laboratory
B、discharges of high-energy electron in the Sun, in exploding stars, and in lightning
C、electrons escaping their normal connections
D、radio waves
答案B
解析 注意题干中的词组"used to"是解题的一个关键，在文章的第二段能找到答案。
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