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In 1997 , he was signed as an amateur free agent by the Arizona Diamondbacks and began his professional career in the Dominican Summer League .
 Arizona Diamondbacks, Dominican Summer League
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Arizona Diamondbacks, Dominican Summer League