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Natural MHD dynamos are an active area of research in plasma physics and are of great interest to the geophysics and astrophysics communities , since the magnetic fields of the earth and sun are produced by these natural dynamos .
 earth, sun
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:
 earth, sun