In what way was the nile both a benefit a disadvantage for egypt?

It provided them with water and fertility as an advantage and was a natural barrier for enemies who would want to attack them. On the other hand it could flood and destroy towns and villages that would have to be built anew. They saw the flooding as the will of the gods and believed that the gods were crying so that's why the Nile flooded.

Its either b or c   i'm leaning towards b though i've heard of them during that time period