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They flew to Seoul on Sunday to brief South Korean officials on their Northern trip .
 Seoul, South Korean, Northern, They, South Korean officials, their
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: organization, person, geographical social political, vehicle, location, weapon, facility 
Text: {0} 
Answer:
 Seoul, South Korean, Northern, They, South Korean officials, their