Floodplains are either formed by erosion or by aggradation.
People might want to live here, because the sediments in the river make the soil rich, which is good for farming. There is also plenty of water around because of the rivers, and the rivers can be a form of transportation. The river can also be a food source.
Seoul is the capital of South Korea and Pyongyang is the capital of North Korea - so this already suggests that Seoul would be more in the South and Pyongyang more in the North - which is true, so the whole statement is false.
They two countries are often referred to with the names of their capitals.
South Africa should be the answer.