Final answer:
Nike refers to China as a "two-billion-foot market" because it recognizes the potential of the Chinese shoe market.
Step-by-step explanation:
Nike's reference to China as a "two-billion-foot market" means that China is a potential future market. While Nike only produces a small portion of its output in China, it recognizes the significant size and potential of the Chinese shoe market. With a population of over two billion people, China represents a vast consumer base that Nike could tap into in the future.