Why did people begin to form unions

Which sequence of events shows how mesopotamia developed? a. people formed divisions of labor. the population grew. agriculture was the basis of the society. b. people built cities. people grew crops. people built canals. c. people made laws. people moved to villages and cities. people lived where crops could grow. d. people settled where crops could grow. the population grew. villages and cities formed. select the best answer from the choices provided a b c d