Love the image for this one. Why does Slovakia/Slovenia question ask about Mediterranean and not just Adriatic? Also it should say "Which of these borders" not "Which of the borders."
The best are those quizes where you have to name like 100 biggest cities in New Zealand or some U.S. state and you can see all answers have been guessed by over 10% of the players. Either it was a lot of the locals taking the quiz or a lot of the cheaters. ;)
Great quiz! Well-chosen pairs and distinguishing features. It's easy if you have some familiarity with the countries of the world, of course, as most regular Jetpunkers do; but these are in fact often confused by non-geography-enthusiasts, and there is space for quizzes of different difficulties here.
I might add Sweden and Switzerland.