2013年GMAT考试阅读模拟试题及答案18
<p>2013年<span word="GMAT">GMAT</span>考试阅读模拟试题及答案汇总</p><p> <span word="Milankovitch">Milankovitch</span> <span word="proposed">proposed</span> <span word="in">in</span> <span word="the">the</span> <span word="early">early</span> <span word="twentieth">twentieth</span> <span word="century">century</span> <span word="that">that</span> <span word="the">the</span> <span word="ice">ice</span> <span word="ages">ages</span> <span word="were">were</span> <span word="caused">caused</span> <span word="by">by</span> <span word="variations">variations</span> <span word="in">in</span> <span word="the">the</span> <span word="Earth">Earth</span>’<span word="s">s</span> <span word="orbit">orbit</span> <span word="around">around</span> <span word="the">the</span> <span word="Sun">Sun</span>. <span word="For">For</span> <span word="sometime">sometime</span> <span word="this">this</span> <span word="theory">theory</span> <span word="was">was</span> <span word="considered">considered</span> <span word="untestable">untestable</span>, <span word="largely">largely</span> <span word="because">because</span> <span word="there">there</span> <span word="was">was</span> <span word="no">no</span> <span word="sufficiently">sufficiently</span> <span word="precise">precise</span> <span word="chronology">chronology</span> <span word="of">of</span> <span word="the">the</span> <span word="ice">ice</span> <span word="ages">ages</span> <span word="with">with</span> <span word="which">which</span> <span word="the">the</span> <span word="orbital">orbital</span> <span word="variations">variations</span> <span word="could">could</span> <span word="be">be</span> <span word="matched">matched</span>.</p><p> <span word="To">To</span> <span word="establish">establish</span> <span word="such">such</span> <span word="a">a</span> <span word="chronology">chronology</span> <span word="it">it</span> <span word="is">is</span> <span word="necessary">necessary</span> <span word="to">to</span> <span word="determine">determine</span> <span word="the">the</span> <span word="relative">relative</span> <span word="amounts">amounts</span> <span word="of">of</span> <span word="land">land</span> <span word="ice">ice</span> <span word="that">that</span> <span word="existed">existed</span> <span word="at">at</span> <span word="various">various</span> <span word="times">times</span> <span word="in">in</span> <span word="the">the</span> <span word="Earth">Earth</span>’<span word="s">s</span> <span word="past">past</span>. <span word="A">A</span> <span word="recent">recent</span> <span word="discovery">discovery</span> <span word="makes">makes</span> <span word="such">such</span> <span word="a">a</span> <span word="determination">determination</span> <span word="possible">possible</span>: <span word="relative">relative</span> <span word="land">land</span>-<span word="ice">ice</span> <span word="volume">volume</span> <span word="for">for</span> <span word="a">a</span> <span word="given">given</span> <span word="period">period</span> <span word="can">can</span> <span word="be">be</span> <span word="deduced">deduced</span> <span word="from">from</span> <span word="the">the</span> <span word="ratio">ratio</span> <span word="of">of</span> <span word="two">two</span> <span word="oxygen">oxygen</span> <span word="isotopes">isotopes</span>, 16 <span word="and">and</span> 18, <span word="found">found</span> <span word="in">in</span> <span word="ocean">ocean</span> <span word="sediments">sediments</span>. <span word="Almost">Almost</span> <span word="all">all</span> <span word="the">the</span> <span word="oxygen">oxygen</span> <span word="in">in</span> <span word="water">water</span> <span word="is">is</span> <span word="oxygen">oxygen</span> 16, <span word="but">but</span> <span word="a">a</span> <span word="few">few</span> <span word="molecules">molecules</span> <span word="out">out</span> <span word="of">of</span> <span word="every">every</span> <span word="thousand">thousand</span> <span word="incorporate">incorporate</span> <span word="the">the</span> <span word="heavier">heavier</span> <span word="isotope">isotope</span> 18. <span word="When">When</span> <span word="an">an</span> <span word="ice">ice</span> <span word="age">age</span> <span word="begins">begins</span>, <span word="the">the</span> <span word="continental">continental</span> <span word="ice">ice</span> <span word="sheets">sheets</span> <span word="grow">grow</span>, <span word="steadily">steadily</span> <span word="reducing">reducing</span> <span word="the">the</span> <span word="amount">amount</span> <span word="of">of</span> <span word="water">water</span> <span word="evaporated">evaporated</span> <span word="from">from</span> <span word="the">the</span> <span word="ocean">ocean</span> <span word="that">that</span> <span word="will">will</span> <span word="eventually">eventually</span> <span word="return">return</span> <span word="to">to</span> <span word="it">it</span>. <span word="Because">Because</span> <span word="heavier">heavier</span> <span word="isotopes">isotopes</span> <span word="tend">tend</span> <span word="to">to</span> <span word="be">be</span> <span word="left">left</span> <span word="behind">behind</span> <span word="when">when</span> <span word="water">water</span> <span word="evaporates">evaporates</span> <span word="from">from</span> <span word="the">the</span> <span word="ocean">ocean</span> <span word="surfaces">surfaces</span>, <span word="the">the</span> <span word="remaining">remaining</span> <span word="ocean">ocean</span> <span word="water">water</span> <span word="becomes">becomes</span> <span word="progressively">progressively</span> <span word="enriched">enriched</span> <span word="in">in</span> <span word="oxygen">oxygen</span> 18. <span word="The">The</span> <span word="degree">degree</span> <span word="of">of</span> <span word="enrichment">enrichment</span> <span word="can">can</span> <span word="be">be</span> <span word="determined">determined</span> <span word="by">by</span> <span word="analyzing">analyzing</span> <span word="ocean">ocean</span> <span word="sediments">sediments</span> <span word="of">of</span> <span word="the">the</span> <span word="period">period</span>, <span word="because">because</span> <span word="these">these</span> <span word="sediments">sediments</span> <span word="are">are</span> <span word="composed">composed</span> <span word="of">of</span> <span word="calcium">calcium</span> <span word="carbonate">carbonate</span> (<span word="calcium">calcium</span> <span word="carbonate">carbonate</span>: <span word="n">n</span>.[化]碳酸钙) <span word="shells">shells</span> <span word="of">of</span> <span word="marine">marine</span> <span word="organisms">organisms</span>, <span word="shells">shells</span> <span word="that">that</span> <span word="were">were</span> <span word="constructed">constructed</span> <span word="with">with</span> <span word="oxygen">oxygen</span> <span word="atoms">atoms</span> <span word="drawn">drawn</span> <span word="from">from</span> <span word="the">the</span> <span word="surrounding">surrounding</span> <span word="ocean">ocean</span>. <span word="The">The</span> <span word="higher">higher</span> <span word="the">the</span> <span word="ratio">ratio</span> <span word="of">of</span> <span word="oxygen">oxygen</span> 18 <span word="to">to</span> <span word="oxygen">oxygen</span> 16 <span word="in">in</span> <span word="a">a</span> <span word="sedimentary">sedimentary</span> <span word="specimen">specimen</span>, <span word="the">the</span> <span word="more">more</span> <span word="land">land</span> <span word="ice">ice</span> <span word="there">there</span> <span word="was">was</span> <span word="when">when</span> <span word="the">the</span> <span word="sediment">sediment</span> <span word="was">was</span> <span word="laid">laid</span> <span word="down">down</span>.</p>
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