One important difference between the Nile River Valley and Mesopotamia was

the Nile flooded at the same time every year as opposed to the unpredictable flooding of the Tigris and Euphrates Rivers. The predictability of the flooding allowed agriculture to become a mainstay in Egyptian cultures that made their homes along the banks of the Nile river. The predictable floods brought fertile soils which signaled the start of the growing season each year.

B) the Nile flooded at the same time every year as opposed to the sporadic and unpredictable flooding of the Tigris and Euphrates Rivers.

Explanation:

The Nile River was different than the Tigris and Euphrates because the Nile flooded at the same time every year as opposed to the sporadic and unpredictable flooding of the Tigris and Euphrates Rivers. This made it easier for Egyptian farmers to know exactly when to plant crops.