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.

Category: TEENS IN BOOKS
Clue: This 15-year-old Dutch skater is the title character of a classic book by Mary Mapes Dodge
hans brinker

Category: MARK ANTONYMS
Clue: The traditional mark of someone who can't sign his name has this opposite in tic-tac-toe
o

Category: THE ONE & ONLY
Clue: He was the one & only U.S. president to take the oath of office aboard an airplane
lyndon johnson