Which are thought to have contributed to the decline of the indus valley civilization? choose all that are correct. a. people moved to more fertile regions of the subcontinent. b. the indus river and its tributaries changed course c. major sandstorms blanketed the cities, forcing people to leave. d. the soil became too salty for crops to grow. e. cities were destroyed by raging fires which factors led to the development of the four river-valley civilizations of mesopotamia, egypt, the indus valley, and china? choose all answers that are correct. a. a nearby river b. the building of villages and cities c. people doing different jobs d. the construction of places of worship e. the ability to communicate widely through writing which ruler broke with the egyptian practice of worshiping many gods and declared that