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In 1915 , he was recruited by his friend Stephen Mather to help publicize the need for an independent national park agency .
 person: Stephen Mather
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: Stephen Mather 
Answer:
 person: Stephen Mather