汽车的驱动力是怎样产生的？
一个对地面的圆周力；这个反作用力即为驱动汽车的发动机将燃料在其内部燃烧放出的热能转变为机械地面又对车轮产生一个向前的反作用力。
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Passage4
Questions16to20arebasedonthefollowingpassage:
Successfulinnovationshavedrivenmanyoldertechnologiestoextinctionandhaveresultedinhigherproductivity,greaterconsumptionofenergy,increaseddemandofrawmaterials,acceleratedflowofmaterialsthroughtheeconomyandincreasedquantitiesofmetalsandothersubstancesinuseeachperson.Thehistoryofindustrialdevelopmentaboundswithexamples.
In1870,horsesandmulesweretheprimesourceofpoweronU.S.farms.Onehorseormulewasrequiredtosupportfourhumanbeingsaratiothatremainedalmostconstantformanydecades.Atthattime,hadanationalcommissionbeenaskedtoforecastthepopulationfor1970,itsanswerprobablywouldhavedependedonwhetheritsconsultantswereofaneconomicortechnologicalturnofmind.Hadtheybeen“economists”,theywouldprobablyhaveprojectedthe1970horsesormulepopulationtobemorethan50million.Hadtheybeen“technologists”,theywouldhaverecognizedthatthepowerofsteamhadalreadybeenharnessedtoindustryandtolearnandoceantransport.Theywouldhaverecognizedfurtherthatitwouldbetheprimesourceofpoweronthefarm.Itwouldhavebeendifficultforthemtoavoidtheconclusionthatthehorseandmulepopulationwoulddeclinerapidly.
16.Accordingtothepassage,whatsuppliedmostofthepoweronU.S.farmsin1870?
A.AnimalsB.HumansC.EnginesD.Water
17.WhichofthefollowingisNOTmentionedbytheauthorasaconsequenceofnewtechnologicaldevelopments?
A.Oldertechnologiesdieaway.
B.ThequalityoflifeisImproved.
C.Overallproductivityincrease.
D.Morerawmaterialsbecomenecessary.
18.Itcanbeinferredfromthepassagethatby1870.
A.technologybegantobemoreeconomical
B.thesteamenginehadbeeninvented
C.theU.S.horsepopulationwasabout10million
D.anationalcommissionwasabout10million
19.Inthesecondparagraph,theauthorsuggeststhat“economists”would.
A.plantheeconomythroughyearlyforecasts
B.failtoconsidertheinfluenceoftechnologicalinnovation
C.valuetheeconomiccontributionoffarmanimals
D.consultthenationalcommissionontheeconomy
20.Whatistheauthor’sattitudetowardchangesbroughtonbytechnologicalinnovations?
A.Heisexcitedaboutthem.
B.Heacceptthemasnatural.
C.Heisdisturbedbythem.
D.Hequestionstheirusefulness.
PartIVTranslation：
IthasabankofelectronicpenswhichwritelikethePresidentwrites,inhisfavoritelightblueink.(PassageOne)