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: U.S. RIVERS 
Clue: The Falls of Saint Anthony stop this mighty river from being navigable north of St. Paul, Minnesota

SOLUTION: the mississippi

PROBLEM: Category: POTPOURRI 
Clue: This chess piece that usually looks like part of a castle is sometimes called a castle

SOLUTION: rook

PROBLEM: Category: YOU MAKE ME CRY 
Clue: 1989's "Harlem Nights" featured this former talk show host as the "Crying Man"

SOLUTION:
arsenio hall