TASK DEFINITION: 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.
PROBLEM: Category: MOZART & FRIENDS 
Clue: Mozart wrote a lovely motet for Venanzio Rauzzini, one of these specially treated singers

SOLUTION: a castrato

PROBLEM: Category: CAPITAL CITY BIRTHPLACES 
Clue: Ilie Nastase

SOLUTION: bucharest, romania

PROBLEM: Category: THE MASON-DIXON LINE 
Clue: As the boundary between slave & free states, the line extended along this river to the Mississippi

SOLUTION:
ohio river