Multiple choice What is the largest and longest river in Indochina? Yangtze River Yellow River Mekong River Yalu River Reveal answer Fill a bubble to check yourself C Correct answer Explanation The Mekong River is the longest river in Southeast Asia, flowing through several countries including Laos, Thailand, Cambodia, and Vietnam. The Yangtze and Yellow rivers are in China, and the Yalu forms the border between China and North Korea.