I want to know the answer to the following question:
Chinese troops attacked the UN forces when they crossed what river?
All the background I'm provided with is that "As UN forces continued to advance toward the Yalu River on the border with Communist China, the Chinese crossed the Yalu River in October and launched a series of surprise attacks that sent the UN forces reeling back across the 38th Parallel.". Is that enough to answer the question?
Answer: yes