How did the physical features of the land and waters in east asia influence the development of the culture?

Given that this area was quite rich in soil and silt, it was easier to survive in these parts than in some other areas in the world. Since the soil was rich and could be processed, farming and agriculture didn't take up a lot of people's time, which is why they could divert their attention to some other things, such as specializing trade, which helped them advance their culture greatly. 

Ithink the answer is d.