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: SCULPTURE 
Clue: Giovanni Bernini sculpted "Apollo and" this nymph for Cardinal Borghese in the 1620s

SOLUTION: daphne

PROBLEM: Category: ROYALTY 
Clue: She has 2 children, David & Sarah Armstrong-Jones

SOLUTION:
princess margaret