Morethanhalfofthewor的精選

問題詳情：Morethanhalfoftheworld’spopulationlivesincities.Trafficandpollutionarebecomingbigproblemsinbigcitiesallovertheworld.IncitieslikeMexicoCity,ShanghaiorCairothequalityoftheairisgettingworseevery...