You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.

Category: U.S. POPULATION 
Clue: Between 2000 & 2010 these 2 states that border each other led the nation in highest percentage of population increase, 35% & 25%
arizona and nevada

Category: U.S. CITIES 
Clue: On May 24, 1844 Samuel Morse was in this city demonstrating his invention
washington, d.c.

Category: THE MAP OF EUROPE 
Clue: Bordering Italy, Austria, Hungary & Croatia, it's one of the world's newest independent countries

slovenia