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From 1981-1985 Lien Khuong Airport served civil service filghts with Ho Chi Minh City - Lien Khuong route ( one filght weekly ) on AK40 Aircraft but all civil flights was suspended due to low passenger traffic .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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