GRE阅读高频机经原文及题目：恐龙灭绝和行星撞地球
<p> 18. 恐龙灭绝和行星撞地球</p><p> <span word="Iridium">Iridium</span>, <span word="a">a</span> <span word="hard">hard</span>, <span word="whitish">whitish</span> <span word="metal">metal</span> <span word="similar">similar</span> <span word="to">to</span> <span word="platinum">platinum</span>, <span word="is">is</span> <span word="extremely">extremely</span> <span word="rare">rare</span> <span word="on">on</span> <span word="Earth">Earth</span>. <span word="Extremely">Extremely</span> <span word="high">high</span> <span word="concentrations">concentrations</span> <span word="of">of</span> <span word="iridium">iridium</span> <span word="on">on</span> <span word="Earth">Earth</span> <span word="result">result</span> <span word="from">from</span> <span word="only">only</span> <span word="two">two</span> <span word="scenarios">scenarios</span>: <span word="massive">massive</span> <span word="volcanic">volcanic</span> <span word="eruptions">eruptions</span> <span word="that">that</span> <span word="release">release</span> <span word="iridium">iridium</span> <span word="from">from</span> <span word="deep">deep</span> <span word="within">within</span> <span word="the">the</span> <span word="Earth">Earth</span> <span word="and">and</span> <span word="meteorites">meteorites</span> <span word="that">that</span> <span word="shower">shower</span> <span word="down">down</span> <span word="on">on</span> <span word="Earth">Earth</span> <span word="from">from</span> <span word="space">space</span>. <span word="When">When</span> <span word="scientists">scientists</span> <span word="found">found</span> <span word="concentrations">concentrations</span> <span word="of">of</span> <span word="iridium">iridium</span> 30 <span word="times">times</span> <span word="higher">higher</span> <span word="than">than</span> <span word="normal">normal</span> <span word="in">in</span> <span word="rock">rock</span> <span word="stratum">stratum</span> <span word="from">from</span> 65 <span word="million">million</span> <span word="years">years</span> <span word="ago">ago</span>, <span word="they">they</span> <span word="concluded">concluded</span> <span word="that">that</span> <span word="a">a</span> <span word="massive">massive</span> <span word="meteor">meteor</span> <span word="or">or</span> <span word="comet">comet</span> <span word="hit">hit</span> <span word="the">the</span> <span word="Earth">Earth</span> <span word="and">and</span> <span word="caused">caused</span> <span word="the">the</span> <span word="massive">massive</span> <span word="extinction">extinction</span> <span word="of">of</span> <span word="the">the</span> <span word="dinosaurs">dinosaurs</span>.</p><p> <span word="Which">Which</span> <span word="of">of</span> <span word="the">the</span> <span word="following">following</span>, <span word="if">if</span> <span word="true">true</span>, <span word="most">most</span> <span word="strongly">strongly</span> <span word="supports">supports</span> <span word="the">the</span> <span word="scientists">scientists</span> <span word="conclusion">conclusion</span>?</p><p> <span word="A">A</span>. <span word="Volcanoes">Volcanoes</span> <span word="massive">massive</span> <span word="enough">enough</span> <span word="to">to</span> <span word="generate">generate</span> <span word="high">high</span> <span word="concentrations">concentrations</span> <span word="of">of</span> <span word="iridium">iridium</span> <span word="are">are</span> <span word="very">very</span> <span word="rare">rare</span>.</p><p> <span word="B">B</span>. <span word="Massive">Massive</span> <span word="volcanic">volcanic</span> <span word="eruptions">eruptions</span> <span word="occurred">occurred</span> <span word="frequently">frequently</span> 80 <span word="million">million</span> <span word="years">years</span> <span word="ago">ago</span>.</p><p> <span word="C">C</span>. <span word="Most">Most</span> <span word="scientists">scientists</span> <span word="support">support</span> <span word="the">the</span> <span word="hypothesis">hypothesis</span> <span word="that">that</span> <span word="a">a</span> <span word="cosmic">cosmic</span> <span word="impact">impact</span> <span word="wiped">wiped</span> <span word="out">out</span> <span word="the">the</span> <span word="dinosaurs">dinosaurs</span>.</p><p> <span word="D">D</span>. <span word="The">The</span> <span word="massive">massive</span> <span word="extinction">extinction</span> <span word="that">that</span> <span word="occurred">occurred</span> 70 <span word="million">million</span> <span word="years">years</span> <span word="ago">ago</span> <span word="killed">killed</span> <span word="not">not</span> <span word="only">only</span> <span word="the">the</span> <span word="dinosaurs">dinosaurs</span> <span word="but">but</span> <span word="also">also</span> 70 <span word="percent">percent</span> <span word="of">of</span> <span word="all">all</span> <span word="life">life</span> <span word="on">on</span> <span word="Earth">Earth</span>.</p><p> <span word="E">E</span>. <span word="A">A</span> <span word="comet">comet</span> <span word="struck">struck</span> <span word="the">the</span> <span word="earth">earth</span> <span word="some">some</span> 120 <span word="million">million</span> <span word="years">years</span> <span word="ago">ago</span>, <span word="but">but</span> <span word="no">no</span> <span word="widespread">widespread</span> <span word="extinction">extinction</span> <span word="occurred">occurred</span>.</p><p> </p>
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