题目内容：
根据以下材料，回答题Nearly,all"speedreading"courseshavea"pacing"element--sometimingdevicewhichletsthestudentknowhowmanywordsaminuteheisreading.Youcandothissimplybylookingatyourwatchevery5or10minutesandnotingdownthepagenumber
youhavereached.Checktheaveragenumberofwordsperpagefortheparticularbookyouarereading.Howdoyouknowwhen5minuteshaspassedonyourwatchifyouarebusyreadingthe
book?Well,thisisdifficultatfirst.Afriendcanhelpbytimingyouoverasetperiod,oryoucanreadwithinhearingdistanceofapublicclockwhichstrikesthequarterhours.Paceyourselfevery
threeorfourdays,alwayswiththesamekindofeasy,generalinterestbooks.Youshouldsoonnoticeyouraccustomedw.p.m,rate
creepingup.
Obviouslythereislittlepointinincreasingyourw.p.m,rateifyoudonotunderstandwhatyouarereading.Whenyouareconsciouslytryingtoincreaseyourreadingspeed,stopafterevery
chapter(ifyouarereadinganovel)oreverysectionorgroupoftenortwelvepages(ifitisatext-book)andaskyourselfafewquestionsaboutwhatyouhavebeenreading.Ifyoufindyouhavelostthethreadofthestory,oryoucannotrememberclearlythedetailsofwhatwassaid,rereadthe
sectionorchapter.
Youcanalsotry"lightningspeed"exercisefromtimetotime.Takefourorfivepagesofthegeneralinterestbookyouhappentobereadingandreadthemasfastasyoupossiblycan.Donotbother
aboutwhetheryouunderstandornot.Nowgobackandreadthematwhatyoufeeltobeyour"normal"w.p.m,rate,therateatwhichyoucancomfortablyunderstand.Aftera"lightningspeed"
readingthrough(probably600w.p.m.),youwillusuallyfindthatyour"normal"speedhasincreased--perhapsbyasmuchas50-100w.p.m.Thisisthetechniquesportsmanusewhentheyusuallyrunfurtherintrainingthantheywillhavetoonthedayofthebigrace.
Accordingtothepassage,a"pacing"device A．isusedtotimethestudent'sreadingspeed
B．isnotusedinmostspeedreadingcourses
C．isusedasanaidtovocabularylearning
D．shouldbeusedwheneverwereadalone
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答案解析：