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According to Galen , these elements were used by Hippocrates in describing the human body with an association with the four humours : yellow bile ( fire ) , black bile ( earth ) , blood ( air ) , and phlegm ( water ) .
 Galen, Hippocrates, black bile
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 Galen, Hippocrates, black bile