What made the Fertile Crescent so fertile?

Question

A.
imported crops brought by foreign traders

B.
moderate temperatures in the summer

C.
heavy snowfalls in winter

D.
silt deposited by annual flooding

Answer 1

From Google:

Named for its rich soils, the Fertile Crescent, often called the “cradle of civilization,” is found in the Middle East. Because of this region’s relatively abundant access to water, the earliest civilizations were established in the Fertile Crescent, including the Sumerians.