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

SOLUTION: chile

PROBLEM: Category: THE "I"s HAVE IT 
Clue: In a proverb, it's "no excuse" for breaking the law

SOLUTION: ignorance

PROBLEM: Category: UH-OH, OPERA 
Clue: This heroine of a 1915 Schillings opera shares her name with a lady painted by Leonardo

SOLUTION:
mona lisa