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Two experiments investigating the effects of short - term spaceflight on cancellous bone turnover were carried out : Physiological Systems Experiment - 1 ( PSE - 1 ) ( a 4 - d orbital spaceflight ) and PSE - 2 ( a 10 - d flight ) .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
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