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In May 2010 , A.M. Best Company affirmed the financial strength rating of A ( Excellent ) of Zenith National Insurance Corp. and its subsidiaries .
 A.M. Best Company, Zenith, Insurance
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 A.M. Best Company, Zenith, Insurance