Final answer:
The Nile River was crucial to the growth of Egyptian civilization, providing fertile soil and predictable flooding, unlike the Tigris and Euphrates Rivers that influenced Mesopotamian civilization.
Step-by-step explanation:
The geographic feature that had a major influence on the development of both Egyptian and Mesopotamian civilizations was A) the Nile River. This river was instrumental in the emergence and growth of Egyptian civilization along its banks and provided a predictable and annual flooding that enriched the soil and supported agriculture. While Mesopotamian civilization developed along the Tigris and Euphrates Rivers, the consistency and predictability of the Nile's floods contributed to Egypt's stable agricultural cycles and thus had a significant influence on the development of its civilization, leading to large cities, grand architecture, and a complex societal structure.