【单选题】
As viewed from space, theEarth’s distinguishing characteristics are its blue waters and white clouds.Enveloped by an ocean of air consisting of 78% nitrogen and 21% oxygen, the planet is the only one in our solar system known to harbor life.Circling the Sun at an average distance of 149 million km (93 million miles), theEarth is the third planet from the Sun and the fifth largest planet in the solar system. Its rapid and molten nickel-iron core give rise to an extensive magnetic field which, coupled with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Most meteors burn up in theEarth’s atmosphere before they can strike the surface. The planet’s active geological processes have left no evidence of the ancient pelting it almost certainly received soon after it was formeD、TheEarth has a single natural satellite-the Moon.
Why does theEarth show almost no signs of having been hit by numerous meteors in the pastA．Humans have built over most of the craters.
B．Most meteors fell into the ocean and not on lanD、
C．TheEarth’s magnetic field repelled most meteors.
D．TheEarth’s natural geologic activity has eliminated most traces.
网考网参考答案：D
网考网解析：暂无解析
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