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: ART & ARTISTS 
Clue: An X-ray of his "Blue Boy" has revealed the figure of a small dog that was painted out

SOLUTION: thomas gainsborough

PROBLEM: Category: VERY JANUARY 
Clue: January is one of this many months in the year with a length of 31 days

SOLUTION: 7

PROBLEM: Category: BELLS 
Clue: 1857 song that includes the line "Bells on bob-tail ring"

SOLUTION:
jingle bells