Translation:I do not live in Bohemia but in Moravia.
I've seen a good explanation in another discussion. I don't recall which one it was, but it was a very similar exercise. As I remember, though the short answer is... Some take "v" and some take "na," and we just need to learn which is which. :-(
= = = UPDATE = = = I found the other discussion! https://www.duolingo.com/comment/25816244