17623
The present study investigates the gene expression changes in human lung alveolar epithelial cells upon exposure to formaldehyde , acrolein and acetaldehyde at sub - cytotoxic levels .
 formaldehyde, acrolein, acetaldehyde
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 formaldehyde, acrolein, acetaldehyde