I was surprised to see Oslo accorded a population of > 1 million and my researches subsequently confirmed me in my opinion as it's poplation appears to be between 600 and 700,000.
Riga no longer has an urban area above 1 million inhabitants most sources listing it above this mark are heavily outdated by +10 years such as https://en.wikipedia.org/wiki/List_of_metropolitan_areas_in_Europe. While the wikipedia page on the city lists it being 939,000
I was surprised when Koln wasn't accepted, as I was pretty sure it crossed 1 million in 2010ish. Then when I finally got Copenhagen, I saw it appear there. Kind of a strange case, but I think I'd accept it as a type-in for the C answer.
Krakow is Poland's second largest city. Katowice is much smaller. I visited both, and trust me, Krakow is much bigger, and feels that way, too. Yet, this accepts Katowice, and not Krakow? Sorry, but I don't think that makes sense. Also, Zagreb is not accepted for Z, and neither Genoa nor Geneva are accepted for G. Maybe they are not technically big enough?
I was trying Utrecht, which probably should be there according to comments. Also, JetPunk quizzes usually spell Yekaterinburg with a Y, even if citypopulation.de uses the German transliteration of Jekaterinburg
how the jesus christ is newcastle-upon-tyne on this list, where did you get your sources? are you including the cities of sunderland, middlesborough and durham in the metropolitan area??
G: Genova and Geneva
Warsawcitypopulation.de/world/Agglomerations.html
https://www.citypopulation.de/en/world/agglomerations/