37881
In 2017 , coal power in the United States provided 30 % of the electricity , down from approximately 49 % in 2008 , due to plentiful supplies of low cost natural gas obtained by hydraulic fracturing of tight shale formations .
 location: United States
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: United States 
Answer:
 location: United States