What were the social structures of the indus valley and egyptian society?

The answer to your question is: Little is known in detail about the societal structure of the ancient Indus Valley inhabitants, because their writings have not been deciphered as of 2014. However, archaeologists have made many discoveries that suggest Indus society was highly egalitarian with a centralized government. Statues and art from that time suggest a high degree of equality with regional leaders forming a central authority.

To prevent the population from overgrowing

Icould be wrong but i would say b.