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In an effort to improve a bullpen that often struggled in 2013 , the Tigers signed veteran closer Joe Nathan to a two-year , $ 20 million contract , with a club option for 2016 , and later signed Joba Chamberlain to a one-year , $ 2.5 million deal .
 organization: Tigers; person: Joe Nathan; person: Joba Chamberlain
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 organization: Tigers; person: Joe Nathan; person: Joba Chamberlain