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: COLLECTIBLES 
Clue: When he moved into the White House, George W. Bush brought some of his over 150 autographed ones of these

SOLUTION: baseballs

PROBLEM: Category: U.S. PRESIDENTS 
Clue: 1 of the 3 U.S. Presidents to run on a third-party ticket after having already served as president

SOLUTION: teddy roosevelt, martin van buren & millard fillmore

PROBLEM: Category: SPORTS & RECREATION 
Clue: Pioneered by pro hockey player Scott Olsen, it had 3 million U.S. participants in 1989 & has 30 million now

SOLUTION:
rollerblading