Final answer:
The Fertile Crescent's fertility was due to its rich soil from seasonal river flooding and advanced irrigation systems that allowed for effective farming.
Step-by-step explanation:
The Fertile Crescent was named for its rich soil and consistent rainfall, which combined to create an environment ideal for agriculture. The region's fertility owed much to the seasonal flooding of the Tigris and Euphrates rivers, which deposited nutrient-rich silt onto the land, enhancing its agricultural potential. Additionally, ancient farmers in this region developed advanced irrigation systems to control and maximize the use of the water from these rivers, which allowed them to continually water their crops and was essential for agricultural success.
Therefore, the correct answer to what made the Fertile Crescent so fertile is a combination of its C: Rich soil and D: Advanced irrigation systems. These factors together enabled the early civilizations within the Fertile Crescent, such as Ur, Babylon, and Nineveh, to thrive by cultivating staple crops like wheat and barley and domesticating animals such as goats, sheep, and cows.