This is apparently based on "https://en.wikipedia.org/wiki/Largest_urban_areas_of_the_European_Union". But see the corresponding talk page for the problems with this data. In any case, the list is for "the European Union", not "Europe".
this quiz is nonsense. Where on earth did those ludicrous figures come from? Birmingham is the UK's second city, not Manchester... Lisbon bigger than either - no way! Milan the largest Italian city??? And Moscow - Europe's biggest city - and Istanbul totally forgotten... please delete this quiz or bring it in line with reality, it's a work of fiction and a waste of time as it stands
Though the way this study was done is clearly questionable with Lisbon being bigger than Birmingam or Manchester, there are other things you mentioned that are actually acceptable. Milan is often considered the biggest city in Italy and the quiz is EU cities which is why some where not on. Birmingham and Manchester are interchangeable depending on how it is measured