gre考试阅读真题解析(B)
<p> <span word="Benjamin">Benjamin</span> <span word="Franklin">Franklin</span> <span word="established">established</span> <span word="that">that</span> <span word="lightning">lightning</span> <span word="is">is</span> <span word="the">the</span> <span word="transfer">transfer</span> <span word="of">of</span> <span word="positive">positive</span> <span word="or">or</span> <span word="negative">negative</span> <span word="electrical">electrical</span> <span word="charge">charge</span> <span word="between">between</span> <span word="regions">regions</span> <span word="of">of</span> <span word="a">a</span> <span word="cloud">cloud</span> <span word="or">or</span> <span word="from">from</span> <span word="cloud">cloud</span> <span word="to">to</span> <span word="earth">earth</span>. <span word="Such">Such</span> <span word="transfers">transfers</span> <span word="require">require</span> <span word="that">that</span> <span word="electrically">electrically</span> <span word="neutral">neutral</span> <span word="clouds">clouds</span>, <span word="with">with</span> <span word="uniform">uniform</span> <span word="charge">charge</span> <span word="distributions">distributions</span>, <span word="become">become</span> <span word="electrified">electrified</span> <span word="by">by</span> <span word="separation">separation</span> <span word="of">of</span> <span word="charges">charges</span> <span word="into">into</span> <span word="distinct">distinct</span> <span word="regions">regions</span>. <span word="The">The</span> <span word="greater">greater</span> <span word="this">this</span> <span word="separation">separation</span> <span word="is">is</span>, <span word="the">the</span> <span word="greater">greater</span> <span word="the">the</span> <span word="voltage">voltage</span>, <span word="or">or</span> <span word="electrical">electrical</span> <span word="potential">potential</span> <span word="of">of</span> <span word="the">the</span> <span word="cloud">cloud</span>. <span word="Scientists">Scientists</span> <span word="still">still</span> <span word="do">do</span> <span word="not">not</span> <span word="now">now</span> <span word="the">the</span> <span word="precise">precise</span> <span word="distribution">distribution</span> <span word="of">of</span> <span word="charges">charges</span> <span word="in">in</span> <span word="thunderclouds">thunderclouds</span> <span word="nor">nor</span> <span word="how">how</span> <span word="separation">separation</span> <span word="adequate">adequate</span> <span word="to">to</span> <span word="support">support</span> <span word="the">the</span> <span word="huge">huge</span> <span word="voltages">voltages</span> <span word="typical">typical</span> <span word="of">of</span> <span word="lightning">lightning</span> <span word="bolts">bolts</span> <span word="arises">arises</span>. <span word="According">According</span> <span word="to">to</span> <span word="one">one</span> <span word="theory">theory</span>, <span word="the">the</span> <span word="precipitation">precipitation</span> <span word="hypothesis">hypothesis</span>, <span word="charge">charge</span> <span word="separation">separation</span> <span word="occurs">occurs</span> <span word="as">as</span> <span word="a">a</span> <span word="result">result</span> <span word="of">of</span> <span word="precipitation">precipitation</span>. <span word="Larger">Larger</span> <span word="droplets">droplets</span> <span word="in">in</span> <span word="a">a</span> <span word="thundercloud">thundercloud</span> <span word="precipitate">precipitate</span> <span word="downward">downward</span> <span word="past">past</span> <span word="smaller">smaller</span> <span word="suspended">suspended</span> <span word="droplets">droplets</span>. <span word="Collisions">Collisions</span> <span word="among">among</span> <span word="droplets">droplets</span> <span word="transfer">transfer</span> <span word="negative">negative</span> <span word="charge">charge</span> <span word="to">to</span> <span word="precipitating">precipitating</span> <span word="droplets">droplets</span>, <span word="leaving">leaving</span> <span word="the">the</span> <span word="suspended">suspended</span> <span word="droplets">droplets</span> <span word="with">with</span> <span word="a">a</span> <span word="positive">positive</span> <span word="charge">charge</span>, <span word="thus">thus</span> <span word="producing">producing</span> <span word="a">a</span> <span word="positive">positive</span> <span word="dipole">dipole</span> <span word="in">in</span> <span word="which">which</span> <span word="the">the</span> <span word="lower">lower</span> <span word="region">region</span> <span word="of">of</span> <span word="the">the</span> <span word="thundercloud">thundercloud</span> <span word="is">is</span> <span word="filled">filled</span> <span word="with">with</span> <span word="negatively">negatively</span> <span word="charged">charged</span> <span word="raindrops">raindrops</span> <span word="and">and</span> <span word="the">the</span> <span word="upper">upper</span> <span word="with">with</span> <span word="positively">positively</span> <span word="charged">charged</span> <span word="suspended">suspended</span> <span word="droplets">droplets</span>.</p><p> 17. <span word="The">The</span> <span word="passage">passage</span> <span word="is">is</span> <span word="primarily">primarily</span> <span word="concerned">concerned</span> <span word="with">with</span> <span word="discussing">discussing</span> <span word="which">which</span> <span word="of">of</span> <span word="the">the</span> <span word="following">following</span>?</p><p> <span word="A">A</span> <span word="central">central</span> <span word="issue">issue</span> <span word="in">in</span> <span word="the">the</span> <span word="explanation">explanation</span> <span word="of">of</span> <span word="how">how</span> <span word="lightning">lightning</span> <span word="occurs">occurs</span></p><p> <span word="Benjamin">Benjamin</span> <span word="Franklins">Franklins</span> <span word="activities">activities</span> <span word="as">as</span> <span word="a">a</span> <span word="scientist">scientist</span></p><p> <span word="Research">Research</span> <span word="into">into</span> <span word="the">the</span> <span word="strength">strength</span> <span word="and">and</span> <span word="distribution">distribution</span> <span word="of">of</span> <span word="thunderstorms">thunderstorms</span></p><p> <span word="The">The</span> <span word="direction">direction</span> <span word="of">of</span> <span word="movement">movement</span> <span word="of">of</span> <span word="electrical">electrical</span> <span word="charges">charges</span> <span word="in">in</span> <span word="thunderclouds">thunderclouds</span></p>
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