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: A WALK ACROSS THE CHARLES BRIDGE 
Clue: Originally called Stone Bridge, the Charles Bridge was built with this "stone", like the walls of the White House
sandstone

Category: POLITICAL QUOTES 
Clue: This financier & advisor to presidents coined the expression “cold war” in 1947
bernard baruch

Category: ROCK'S FRONTMEN & WOMEN 
Clue: Ozzy Osbourne

black sabbath