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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 2026.
    Finding life on Mars would be an epochal【C19】________The rights that go with being first to make the find is part of what makes the planet the hot new【C20】________.
【C4】
选项 A、when
B、as
C、since
D、while
答案D
解析 连词辨析题。四个选项分别为A项when“当……时(主句和从句的动作同时发生或有先后发生，常接短暂性动词)”；B项as“正当……时，随着(主句和从句动作同时或先后发生，可以接延续性或短暂性动词)”；C项since“自……以来”，D项while“在……期间 (强调持续性的动作同时进行)”。根据原文“执行绕火星飞行________研究火星大气层为期至少两年的任务”可知，在绕火星飞行的同时研究火星大气层，强调两个动作在同一时期发生且延续时间较长，故答案为D项。
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