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In January 2015 , Stephen Hawking , Elon Musk , and dozens of artificial intelligence experts signed an " open letter on artificial intelligence " calling for research on the societal impacts of AI .
 person: Stephen Hawking; person: Elon Musk
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
 Entities: Stephen Hawking, Elon Musk 
Answer:
 person: Stephen Hawking; person: Elon Musk