Answer:
The river valleys helped civilizations prosper because of the fertile soil which allowed the civilizations to grow an ample amount of food to support their growing community. Another way it helped the civilization expand was by giving ease of transportation and trade. The river allowed products (or people) to move quicker and easier, therefore, helping out overall. Another example was that there was a constant source of clean drinking water for the civilians
Step-by-step explanation:
It's been a while so I dont know.