- 问题详情:Imaginearoadcrossingwithoutthethree-waytrafficsignal.Cars,trucks,schoolbuses,bicyclistsandstudentswalkingtoschoolwouldtrytorushthroughthecrossing61_______thesametime.Theirsafetywouldbeindanger.ThankstoanAfricanAmerican62________(invent)namedG...
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