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Transcriptome analysis was performed to identify changes introduced by culture at different oxygen concentrations ( 20 % , 40 % , 60 % , and 80 % of oxygen ) .
 Chemical: oxygen; Chemical: oxygen
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: oxygen; Chemical: oxygen