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: BUMPED FROM THE COVER OF TIME 
Clue: A cover titled "Declining American Birthrate" was canceled in 1974 when this man was pardoned

SOLUTION: richard m. nixon

PROBLEM: Category: THE BODY HUMAN 
Clue: This pancreatic hormone is produced in specialized cells in the Islets of Langerhans

SOLUTION:
insulin