This is what I found on the city name of Porto above. "Oporto" seems to be quite an odd one to include when there are so many other 'O' cities to choose from, the Portuguese don't refer to the city as Oporto and now foreign people don't either, it was only called Oporto due to peoples well meaning ignorance. It should not be in this quiz at all!
that the capitol city was Monte Carlo.
Though besides antwerp, which is antwerpen in its own language the other ones are the same in their native language.
I'd like to offer some alternatives:
Czech City neighbouring Poland - Ostrava
Ukraine's "Pearl of the black sea" - Odessa
Largest city on Gulf of Bothnia - Oulu