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-DOCSTART- The collective heart of our @houstonpolice & amp ; American first responder community is second to none . We are proud to serve . https://t.co/aIvoqvPXf5
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: exact location, area, road, river 
Text: {0} 
Answer:
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