Answer:
These three civilizations were all centered around rivers that flooded regularly.
Step-by-step explanation:
In ancient times, to prosper, civilization should be closer to rivers. Most important, it was necessary to understand how the floods work and, then, be adaptative to each situation. In the case of the civilzations that you asked:
- Egypt: the Nile has an abundance when it comes to its floods. The period when the waters rise is June to September and then when they turn back, they fertilize the earth with hummus (a fertile mud). Then, Egyptians can plant.
- Sumer: the same thing occurs with the Tigris and Euphrates rivers, where the Sumerian cities were located.
- Harappa: in this case, is with the Indus River.