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The Oakland Athletics MLB club won three consecutive World Series championships in 1972 , 1973 , and 1974 , and appeared in another three consecutive World Series from 1988 to 1990 , winning their fourth championship in 1989 .
 Oakland Athletics MLB
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Oakland Athletics MLB