Just a thought...if the original question INSISTS on capital cities and the answer is 'have hosted the games' then the answer is Paris as Antwerp is not a capital as pointed out by fordward. It also would explain why St. Louis is missing from the question sequence.
When I posted my answer, as the only information was as given, had no idea how many letters and nothing about the Olympic Games, I was just working on capital European cities from South to North. However being a wrinklie myself perhaps it was just another senior moment.