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Formaldehyde gave the strongest response ; a total of 66 genes were more than 1 . 5 - fold differentially expressed mostly involved in apoptosis and DNA damage related processes , followed by acetaldehyde ( 57 genes ) , hydroquinone ( 55 genes ) and nicotine ( 8 genes ) .
 Formaldehyde, acetaldehyde, hydroquinone, nicotine
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Formaldehyde, acetaldehyde, hydroquinone, nicotine