六级冲刺练习：阅读（51）
<p> <span word="Sagan">Sagan</span> <span word="believes">believes</span> <span word="that">that</span> <span word="before">before</span> <span word="the">the</span> <span word="earths">earths</span> <span word="resources">resources</span> <span word="are">are</span> <span word="completely">completely</span> <span word="exhausted">exhausted</span> <span word="it">it</span> <span word="will">will</span> <span word="be">be</span> <span word="possible">possible</span> <span word="to">to</span> <span word="change">change</span> <span word="the">the</span> <span word="atmosphere">atmosphere</span> <span word="of">of</span> <span word="Venus">Venus</span> <span word="and">and</span> <span word="so">so</span> <span word="create">create</span> <span word="a">a</span> <span word="new">new</span> <span word="world">world</span> <span word="almost">almost</span> <span word="as">as</span> <span word="large">large</span> <span word="as">as</span> <span word="earth">earth</span> <span word="itself">itself</span>. <span word="The">The</span> <span word="difficulty">difficulty</span> <span word="is">is</span> <span word="that">that</span> <span word="Venus">Venus</span> <span word="is">is</span> <span word="much">much</span> <span word="hotter">hotter</span> <span word="than">than</span> <span word="the">the</span> <span word="earth">earth</span> <span word="and">and</span> <span word="there">there</span> <span word="is">is</span> <span word="only">only</span> <span word="a">a</span> <span word="tiny">tiny</span> <span word="amount">amount</span> <span word="of">of</span> <span word="water">water</span> <span word="there">there</span>.</p><p> <span word="Sagan">Sagan</span> <span word="proposes">proposes</span> <span word="that">that</span> <span word="algae">algae</span> <span word="organisms">organisms</span>, <span word="which">which</span> <span word="can">can</span> <span word="live">live</span> <span word="in">in</span> <span word="extremely">extremely</span> <span word="hot">hot</span> <span word="or">or</span> <span word="cold">cold</span> <span word="atmospheres">atmospheres</span> <span word="and">and</span> <span word="at">at</span> <span word="the">the</span> <span word="same">same</span> <span word="time">time</span> <span word="produce">produce</span> <span word="oxygen">oxygen</span>, <span word="should">should</span> <span word="be">be</span> <span word="bred">bred</span> <span word="in">in</span> <span word="conditions">conditions</span> <span word="similar">similar</span> <span word="to">to</span> <span word="those">those</span> <span word="on">on</span> <span word="Venus">Venus</span>. <span word="As">As</span> <span word="soon">soon</span> <span word="as">as</span> <span word="this">this</span> <span word="has">has</span> <span word="been">been</span> <span word="done">done</span>, <span word="the">the</span> <span word="algae">algae</span> <span word="will">will</span> <span word="be">be</span> <span word="placed">placed</span> <span word="in">in</span> <span word="small">small</span> <span word="rockets">rockets</span>. <span word="Spaceships">Spaceships</span> <span word="will">will</span> <span word="then">then</span> <span word="fly">fly</span> <span word="to">to</span> <span word="Venus">Venus</span> <span word="and">and</span> <span word="fire">fire</span> <span word="the">the</span> <span word="rockets">rockets</span> <span word="into">into</span> <span word="the">the</span> <span word="atmosphere">atmosphere</span>. <span word="In">In</span> <span word="a">a</span> <span word="fairly">fairly</span> <span word="short">short</span> <span word="time">time</span>, <span word="the">the</span> <span word="algae">algae</span> <span word="will">will</span> <span word="break">break</span> <span word="down">down</span> <span word="the">the</span> <span word="carbon">carbon</span> <span word="dioxide">dioxide</span> <span word="into">into</span> <span word="oxygen">oxygen</span> <span word="and">and</span> <span word="carbon">carbon</span>.</p><p> <span word="When">When</span> <span word="the">the</span> <span word="algae">algae</span> <span word="have">have</span> <span word="done">done</span> <span word="their">their</span> <span word="work">work</span>, <span word="the">the</span> <span word="atmosphere">atmosphere</span> <span word="will">will</span> <span word="become">become</span> <span word="cooler">cooler</span>, <span word="but">but</span> <span word="before">before</span> <span word="man">man</span> <span word="can">can</span> <span word="set">set</span> <span word="foot">foot</span> <span word="on">on</span> <span word="Venus">Venus</span> <span word="it">it</span> <span word="will">will</span> <span word="be">be</span> <span word="necessary">necessary</span> <span word="for">for</span> <span word="the">the</span> <span word="oxygen">oxygen</span> <span word="to">to</span> <span word="produce">produce</span> <span word="rain">rain</span>. <span word="The">The</span> <span word="surface">surface</span> <span word="of">of</span> <span word="the">the</span> <span word="planet">planet</span> <span word="will">will</span> <span word="still">still</span> <span word="be">be</span> <span word="too">too</span> <span word="hot">hot</span> <span word="for">for</span> <span word="men">men</span> <span word="to">to</span> <span word="land">land</span> <span word="on">on</span> <span word="it">it</span> <span word="but">but</span> <span word="the">the</span> <span word="rain">rain</span> <span word="will">will</span> <span word="eventually">eventually</span> <span word="fall">fall</span> <span word="and">and</span> <span word="in">in</span> <span word="a">a</span> <span word="few">few</span> <span word="years">years</span> <span word="something">something</span> <span word="like">like</span> <span word="earth">earth</span> <span word="will">will</span> <span word="be">be</span> <span word="reproduced">reproduced</span> <span word="on">on</span> <span word="Venus">Venus</span>.</p><p> 21. <span word="In">In</span> <span word="the">the</span> <span word="long">long</span> <span word="run">run</span>, <span word="the">the</span> <span word="most">most</span> <span word="difficult">difficult</span> <span word="problem">problem</span> <span word="caused">caused</span> <span word="by">by</span> <span word="population">population</span> <span word="growth">growth</span> <span word="on">on</span> <span word="earth">earth</span> <span word="will">will</span> <span word="probably">probably</span> <span word="be">be</span> <span word="the">the</span> <span word="lack">lack</span> <span word="of">of</span>______.</p><p> <span word="A">A</span>. <span word="food">food</span> <span word="B">B</span>. <span word="oil">oil</span></p><p> <span word="C">C</span>. <span word="space">space</span> <span word="D">D</span>. <span word="resources">resources</span></p><p> 22. <span word="Carl">Carl</span> <span word="Sagan">Sagan</span> <span word="believes">believes</span> <span word="that">that</span> <span word="Venus">Venus</span> <span word="might">might</span> <span word="be">be</span> <span word="colonized">colonized</span> <span word="from">from</span> <span word="earth">earth</span> <span word="because">because</span>______.</p><p> <span word="A">A</span>. <span word="it">it</span> <span word="might">might</span> <span word="be">be</span> <span word="possible">possible</span> <span word="to">to</span> <span word="change">change</span> <span word="its">its</span> <span word="atmosphere">atmosphere</span></p>
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