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  3. On the surface, Mars is the picture of desolation. A barren land remains【C1】______for hundreds of millions of years, motionless【

On the surface, Mars is the picture of desolation. A barren land remains【C1】______for hundreds of millions of years, motionless【

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问题     On the surface, Mars is the picture of desolation. A barren land remains【C1】______for hundreds of millions of years, motionless【C2】______the scattering of powdery dust by a faint breeze. But perhaps just【C3】______the Martian soil, the picture is very different.
    New evidence suggests the presence of a lake one mile beneath the ice-coated surface of Mars’s south【C4】______, according to new research published Wednesday in Science. Scientists say the lake【C5】______20 kilometers across, and is one meter in【C6】______The findings, if【C7】______, would mark the detection of the largest body of【C8】______water on Mars today.
    The data comes from Mars Express, a European spacecraft that【C9】______Mars for 15 years.【C10】______a high-resolution camera snapped stunning images of the surface, a radar instrument probed what was【C11】______underground.
    The instrument—the Mars Advanced Radar for Subsurface and Ionosphere Sounding, or MARSIS【C12】______—emits radio waves toward the planet. The waves penetrate the Martian surface and bounce off【C13】______material they come in contact with, then reflect back to the spacecraft. MARSIS【C14】______the echoes of the radio waves, which scientists can then【C15】______to decipher the composition of the subsurface.
    Starting in May 2012, MARSIS【C16】______more than three years pinging a region at Mars with radio waves.【C17】______helps to look at the data yourself. In addition to an illustration that shows how Mars Express【C18】______Mars, the image【C19】______what’s called a radargram, a picture of different materials, molded out of radio waves. The thick, gray line at the top is the planet’s surface. The squiggles below that are a【C20】______of ice and dust.
【C9】
选项 A、has being orbited
B、orbited
C、has been orbiting
D、is orbiting
答案C
解析 语法题。首先我们要考虑后半句话的for 15 years，这个时间状语提示需要用完成时态，同时也需要整体考虑全文的时态，全文采取的是现在时，因此这里使用现在完成时即可，观察选项可知，唯一符合现在完成时条件的是[C]。现在完成进行时表示过去发生的事情对现在产生影响，并且影响还会持续下去。在此表示本探测器还会继续工作，没有停止，因此应该选择[C]。
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