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: DIMENSIONS 
Clue: Don't lose the thread--there are 10 or so dimensions in this physics theory
string theory

Category: BORDERS 
Clue: Argentina's border with this country is 3,200 miles long, about the same as its coastline
chile

Category: TEENS OF THE PAST 
Clue: Niccolo Paganini was only 13 when he began composing pieces for this instrument

violin