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: ON THE ROCKS 
Clue: This rock formed from hardened lava formed the Hawaiian Islands

SOLUTION: basalt

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: A McCATEGORY 
Clue: You may remember this '50s senator from Wisconsin from such witch-hunts as "The Red Scare"

SOLUTION:
mccarthy