Final answer:
China sent troops to help North Korea during the Korean War.
Step-by-step explanation:
The correct answer is OD. China. China sent troops to help North Korea during the Korean War. The Chinese troops, also known as the People's Volunteer Army, intervened in the war to support North Korea against the United Nations forces led by the United States. Their entry into the conflict had a significant impact on the course of the war.
Learn more about China's involvement in the Korean War