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  3. Traveling to Mars is usually a【C1】________business—with a single spacecraft taking off from a single launchpad for the seven-mon

Traveling to Mars is usually a【C1】________business—with a single spacecraft taking off from a single launchpad for the seven-mon

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问题     Traveling to Mars is usually a【C1】________business—with a single spacecraft taking off from a single launchpad for the seven-month trip to the Red Planet. That appeared to be the case again on July 30, when NASA’s Perseverance rover roared【C2】________the pad at Cape Canaveral. But this time the ship will have plenty of【C3】________
    On July 19, the United Arab Emirates made its first bid to join the Mars game, launching the "Hope" spacecraft on a mission to orbit Mars for at least two years【C4】________studying its atmosphere. Four days later, China launched its "Questions to Heaven" spacecraft, a three-part ship【C5】________an orbiter, a lander and a six-wheel rover. And a fourth mission, a joint Russian-European project, ExoMars, 【C6】________a rover of its own, was also planned for this summer, though it has been【C7】________to 2022 because of engineering problems with its parachute and avionics.
    So why all the interest in Mars—and why right now? The timing issue has【C8】________to do with planetary mechanics. As they fly their differing solar orbits—Earth on the inner track, Mars on the outer—the distance between the two worlds is forever changing. At their greatest remove, when they are on【C9】________sides of the sun, they are up to 250 million miles apart. But once every two years, they line up on the same side of the sun, with just 35 million miles separating them. This summer just such an alignment is taking place, dramatically slashing inter planetary travel time to the current seven-month itinerary.   So that explains the【C10】________question.
    The why part is because of Mars’ tantalizing,【C11】________biological history. The surface of the planet is etched with dry riverbeds, stamped with ancient sea basins, marked by deep depressions that could only【C12】________long-vanished water.
    Perseverance is landing in one such place: the Jezero Crater, north of the Martian equator, which is lined with both inflow and outflow channels showing it was once a vibrant sea. Previous rover analyses in similar locations have discovered chemicals and【C13】________that form only in the【C14】________of water, proving that Mars was once, like Earth,【C15】________wet.
    Now the mission is to look for actual fossilized organisms or even【C16】________of extant microbial life. To that end, Perseverance is the most ambitious of the new spacecraft and is actually just the first part of a multipart mission. During its explorations, it will【C17】________Martian soil samples and set them neatly on the ground【C18】________another spacecraft that could leave Earth as early as the 2026.
    Finding life on Mars would be an epochal【C19】________. The bragging rights that go with being first to make the find is part of what makes the planet the hot new【C20】________
【C10】
选项 A、when
B、what
C、who
D、how
答案A
解析 词汇辨析题。四个选项分别为[A]when“何时”；[B]what“什么”；[C]who“谁”；[D]how“怎样”。空格处所在句意为“这也就解释了探测火星的________问题”，前文提及“为何众多国家都在此时对火星探测感兴趣”的问题，由此可知空格处所填词应有“时间”之意，故答案为选项[A]。
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