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  3. When Neil Armstrong and Buzz Aldrin returned from the moon, their cargo included nearly fifty pounds of rock and soil, which wer

When Neil Armstrong and Buzz Aldrin returned from the moon, their cargo included nearly fifty pounds of rock and soil, which wer

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问题     When Neil Armstrong and Buzz Aldrin returned from the moon, their cargo included nearly fifty pounds of rock and soil, which were packed in an aluminum box with seals designed to maintain the lunar surface’s low-pressure environment. But back at Johnson Space Center, in Houston, scientists discovered that the seals had been【C1】________—by moon dust.
    Lunar dust is fine, like a powder,【C2】________it cuts like glass. It’s formed when shooting stars【C3】________on the moon’s surface, heating its rocks and dirt and reducing them to fine particles. Since there’s no wind or water to smooth【C4】________edges, the tiny grains are sharp and uneven, and【C5】________nearly everything.
    "The intruding【C6】________of lunar dust represents a more challenging engineering design issue, as well as a【C7】________issue for settlers, than does radiation," wrote Harrison Schmitt, an Apollo 17 astronaut, in his 2006 book, "Return to the Moon." The dust damaged space-suits and ate away layers of moon boots. Over the【C8】________of six Apollo missions, not one rock box【C9】________its vacuum seal. Dust followed the astronauts back into their ships, too. According to Schmitt, it smelled like gunpowder and made breathing【C10】________. No one knows precisely what the extremely small particles do to human lungs.
    The dust not only【C11】________the moon’s surface, but floats up to sixty miles【C12】________it—as an outer part of its atmosphere, where particles【C13】________the moon by gravity, but are so thin that they【C14】________collide. In the nineteen-sixties, Surveyor probes filmed a glowing cloud floating just above the lunar surface during sunrise. Later, Apollo 17 astronaut Gene Cernan, while orbiting the moon, recorded a【C15】________phenomenon at the sharp line where lunar day meets night. Cernan【C16】________a series of pictures illustrating the changing【C17】________; streams of particles popped【C18】________the ground and hovered, and the resulting cloud came into sharper focus as the astronauts’ orbiter approached daylight. Since there’s no wind to form and【C19】________the clouds, their origin is something of a mystery. It’s【C20】________that they’re made of dust, but no one fully understands how or why they do their thing.
【C12】
选项 A、above
B、across
C、on
D、through
答案A
解析 本句提到月尘floats up to sixty mile(漂浮到6英里外)，说明它在月球表面之上的空中。A项above“在……之上(上方)”符合语义逻辑。B项across和D项through均可表示“穿过”，没有线索表明月尘穿过月球表面。C项on虽表示“在……之上(上面)”，但与某物表面接触，与floats up to sixty mile不符。
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