I came here to say this too. As you go on you have to remember the order of the continents and mentally weed out the continents that wouldn't have one for that letter. The yellow box isn't needed; no capitals have duplicate names.
I disagree with above comments. Just got 100% on mobile with plenty of time to spare. It’s true you need to remember the order of the continents, but if you can’t remember a sequence of six you’ll struggle to get 100% anyway. Of course it helps if you can reel off every world capital unprompted, but these quizzes aren’t supposed to be too easy
Maybe mention this in the intro?
It's almost unplayable with the yellow box.
...I've been living in Morocco for the last two years.