题目内容：
根据以下材料，回答题Bicyclesharingsystemsarealsoknownasyellowbicycleprograms,whitebicycleprograms,publicbikesorfreebikes.TheyareincreasinglypopularinEuropenow.Parishastheworld'slargesturban
cyclerentalsystem.
ThisisabikerentalstationinParis.Theworkersareshowinghowtouseanewself-servicebike.TheysaythatPariswillbecome"agreencapitalofbikes"andtheyplantopark20,000bicy-clesat1,600stations.Pariscreatedthisplantoreducewastegasdisplacement(废弃排放量).
Atarentalstation,youonlyhavetoputyourcreditcardintothemachinetorentabike.Itpro-videsFrench,German,EnglishandChineseservices.Ifyouridethebikeforonly30minutestore-lax,youneedn'tpayforit.Atwo-hourbikerentonlycostsyou4Euros.
Thesestationsworkfor24hourseveryday,soabikeisrentedfor10to14timesaday.Inthiswaythereare200,000peopleusingbikesaday.
Inthepastfewyears,Parishasencourageditspeopletoridebikes,butsomethingunhappyhashappenednowandthen.Somepeoplebreakthetrafficrulesduringrushhours.Someparktheirbikes
everywhere.SohowtoparktheirbikesisaproblemthatPairswillface,butthisprojectisstillahelpfulwaytoimproveitstrafficenvironment.
WhydidParisbuildmanyrentalsystems? A．Toreduceaccidents
B．Toimprovethetrafficenvironment
C．Torelaxtravelers
D．Toattracttravelersfromothercountries
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答案解析：