I am pretty sure that the answer is c The Nile flooded every year, which made an otherwise arid desert fertile for agriculture. PLEASE CORRECT ME IF IM WRONG.
Explanation:
I say this because the nile would flood every year wich helped the egyptians with agriculture.
During times of civic unrest such as riots, the national government can summon the national guard to its help if it thinks that the local forces cannot stop it or if the riots are going out of hand.
