The correct answer is - A. Seoul grew much more rapidly.
Even though both New York and Chicago has had relatively quick growth rate since the 19th century, they can not match the tempo of growth rate of modern Seoul. After the end of the World War II, Seoul's population skyrocketed. Prior to the war, the city had walls around it, and the space for living was not changing, thus the population was relatively stable and with the same size. After the war though, the removed walls, foreign influence, and more open attitude, led to dramatic growth rate of the city. From being a city that had bellow one million citizens, Seoul grew to have almost 10 million people nowadays, and that has happened in a period of only around 70 years.