The correct answer is - A. They constructed the Aswan Dam to eliminate seasonal flooding.
By making the decision to construct a dam on the Nile River, the Aswan Dam, the Egyptian government changed the natural order of functioning of the river and it heavily affected the areas near to the river. The most affected of all was the agriculture. That was due to the stopping of the annual floods that the Nile had, with which it was leaving a lot of fertile deposits alongside it, and also increased the levels of the ground waters. Since the Aswan Dam was built, there are no more floods by the Nile, so the agriculture had to switch to other methods in order to develop.
Also, a big problem emerged with the dam because it had restricted the movement of the organism in the river.