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: THE "I"s HAVE IT 
Clue: Style of the 1877 painting seen here
impressionism

Category: SICKNESS & HEALTH 
Clue: The initials HMO, which have stood for heart minute output, now also stand for this
health maintenance organization

Category: NORSE MYTHOLOGY 
Clue: This palace, whose name means "hall of the slain", had walls of gold & a roof of battle shields

valhalla