In1800,onlythreepercentoftheworld'spopulationlivedincit...
问题详情：In1800,onlythreepercentoftheworld'spopulationlivedincities.Onlyonecity—Beijing—hadapopulationofoveramillion.Mostpeoplelivedinruralareas,andneversawacityintheirlives.In1900,justahundredyears...