The correct answer is - Han River.
The Han River is one of the biggest rivers on the Korean Peninsula. The river passes through the capital of South Korea, Seoul, and also forms part of the boundary between North Korea and South Korea with its delta.
This river has a big importance for the Koreans, both in the past and in the present. Historically, this river has been the place where the Three Kingdoms were formed. It has been heavily used for trade, both in the past and in the present, as the river was and still is navigable. And it is worth to mention, that the Han River provides drinking water for over 12 million people in South Korea.