Final answer:
The Nile River floods fertilized the farmland in the river valley, which was a critical advantage for ancient Egyptian agriculture, allowing for plentiful harvests and the growth of their civilization.
Step-by-step explanation:
Among the given options, the advantage of the Nile River floods for the people of ancient Egypt that can be described is A. Fertilized the farmland in the river valley. The seasonal flooding of the Nile deposited rich, fertile silt on the riverbanks, which made the surrounding land extremely arable. This natural irrigation and fertilization allowed the ancient Egyptians to successfully harvest crops, leading to an abundance of food and the capability to support a growing population. The regularity of these floods was so crucial to the development of Ancient Egyptian civilization that it influenced their religious beliefs, with the Nile associated with the concept of Ma'at, which denoted harmony and order in the universe.