This Eastern European nation has humorously offered to build a military base for U.S. forces, calling it Fort Trump. Much of its territory is part of the North European Plain, except for its southern border regions along the Carpathian Mountains. The northeastern part of this nation is adjacent to the Russian exclave of Kaliningrad. For 10 points, name this Eastern European nation with cities like Krakow, Gdansk, and Warsaw as its capital.
a) Hungary
b) Poland
c) Romania
d) Czech Republic