Answer:
C. arable land in river valleys.
Step-by-step explanation:
Southeastern China, sometimes known as China proper, is a very populated area. This has been the case for most of Chinese history. The main reason for this is the fact that this region exhibits densely populated fertile river valleys (along the Yangtze river), which in turn leads to fertile farmland that can support a large population. The area also has plenty of fresh water and a warm, moderate climate.