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: FROM B TO C 
Clue: A group of nations acting together, like the old Soviet one
bloc

Category: I HEAR A SYMPHONY 
Clue: Mozart's 38th is called by the name of this city that stood in for Vienna in the filming of "Amadeus"
prague

Category: 5-LETTER WORDS 
Clue: It's a ballroom dance or the music for the dance, like the "Blue Danube" one

a waltz