Answer:
D.The reliance of China on food imports
Step-by-step explanation:
China has always been a very heavily populated country, in fact, during most of human history, it has been the most populated country in the world, and even if China has a very fertile plain in the middle of the country, the domestic agricultural output has often been insufficient to feed the Chinese Population.
For this reason, China has relied on imports throughout history, and Vietnam has been one of the most important sources of those imports, because of the geographical proximity. Champa rice, a staple Vietnamese product, found its way to China in this manner.