题目内容：
根据以下材料，回答题Themenwhoracethecarsaregenerallysmall,withatight,nervouslook.Theyrangefromtheearly20stothemiddle40s,anditisusuallytheirnervesthatgofirst.
Fearisthedriver'sconstantcompanion,andtragedycanbejustastepbehind.Scarcelyamaninthe500doesnotcarrythescarsofancientcrashes.Themarkoftheplasticsurgeonisevery-where,andburnedskiniscommon.Sometimesadriver'sscarsareinvisible,partofhisheritage.Twoyoungdrivers,BillyVukovichandGaryBettenhausen,racedintheirfirst500in1968.Lessthan
20yearsbefore,theirfathersalsocompetedagainstoneanotherontheIndytrack--anddiedthere.
Allthisthedriversaccept.Overtheyears,theyhavelearnedtotrusttheirowntechniques,reflexes,andcourage.Theydepend,too,onatrustedservant--scientificengineering.Thoughthemaynothavehadagreatdealofschooling(anexceptionisNewZealand'sBruceMcLaren,whohasanengineeringdegree),manydriversaregiftedmechanics,
withafeelingfortheirenginesthatamounttokinship.
Afewtopdrivershavebecomeextremelywealthy,withsix-figureincomesfromprizemoney,endorsements,andjobswithauto-productmanufacturers.Somehavebusinessesoftheirown.McLarendesignsracingchassis.DanGurney'sCaliforniafactorymanufacturedthechassisofthreeofthefirstfourearsinthe1968Indy
500,includinghisownsecondplacecar.
Yetmoneyisnottheonlyreasonwhymenracecars.Perhapsitisn'teventhemajorreason.Three-timeIndywinner(1961,1964,1967)A.J.Foyt,forexample,canfrequentlybefoundcompetingondirtytracksinminor-leagueraces,wheremoney,crowdsandsafetyfeaturesarelimit-ed,andonlythedangerisnot.Whydoeshedoit.'?SometimesFoytanswers,"It'sinmyblood."Othertimeshesays,"Itisgoodpractice."Nowandthenhereplies,"Don'taskdumbquestions."
Thestatement"itisusuallytheirnervesthatgofirst"means A．atfirsttheyallhaveanervouslook
B．theyoftenfindtheycan'tbearthetensioneveniftheyareingoodcondition
C．somedaytheyfindtheycan'tmakeresponsestoanyrisk
D．theycancontinuetheircareeratmostuntilthemiddle40s
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答案解析：