In what country does the River Mekong originate?

Explanation

Mekong is a river in Asia. From the Tibetan Plateau it runs through China, Burma (Myanmar), Laos, Thailand, Cambodia and Vietnam. It is the 12th longest in the world, estimated at length of 4,350-4,909 km. The reason why it can't be measured more exactly is that the river springs from a difficult to access area, where more, smaller rivers form one big one.