Answer:
b. Because of the fertile soil.
Step-by-step explanation:
Having fertile soil is one of the most important requirements for the settlement of humans. This is because settlements depend on agriculture for their survival. Therefore, most major civilizations have began in areas with fertile soil (like along rivers such as the Tigris, Euphrates and Nile). In the case of Southeast Asia, volcanic islands are extremely fertile due to the amount of minerals present in the soil. Similarly, river deltas are extremely fertile areas for agriculture.