5989
In a subcohort of 1009 twin pairs , up to 22 % of the variation in physical fitness and 27 % to 39 % of the variation in muscle strength was attributable to environmental factors unique to one twin ; eg , physical activity .
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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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