9982
A total of 25 nonsmokers ( control group ) and 50 long - term cigarette smokers ( smoking for at least 15 years ; smoker group ) were participated in the study .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None