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: ART 
Clue: Medieval artists gave triangular ones to the trinity, round to the angels & rectangular to living holy people
halos

Category: CRUSADER 
Clue: Pope Urban II said anyone going to liberate this city for devotion alone, not booty, can do it instead of any penance
jerusalem

Category: MEDICINE 
Clue: Hemophilia is a hereditary condition in which this coagulates extremely slowly

blood