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.

[Q]: Category: ART & ARTISTS 
Clue: An X-ray of his "Blue Boy" has revealed the figure of a small dog that was painted out
[A]: thomas gainsborough


[Q]: Category: MILITARY TRAINING BASES 
Clue: Service branch with a San Diego recruit depot & a Yuma air station
[A]: marines


[Q]: Category: AN OPERATIC CATEGORY 
Clue: This Valkyrie was Wotan's favorite daughter
[A]:
brunhilde