Where and how did river basins contribute directly to the emergence of cities, from 3500-2000 bce? what were some similarities and differences in irrigation techniques among these early civilizations?

The service industry in the united states grew in the late 1800s. what was one effect of that growth? the number of people with jobs in factories as unskilled workers decreased. the number of people with jobs in factories as unskilled workers increased. the middle class grew as people took jobs as clerks, lawyers, and teachers. the middle class shrank as people left jobs as clerks, lawyers, and teachers.