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Three main approaches are being used : the measurement of DNA repair gene expression after exposure , although it has not yet been clearly established whether gene expression is indicative of repair capacity ; the monitoring of DNA damage removal by following DNA repair kinetics ; and the modulation of DNA repair activity following exposure in situ , in order to assess the impact of exposure history on DNA repair capacity .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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