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The 15q25 gene cluster contains genes that code for the alpha 5 , alpha 3 , and beta 4 nicotinic acetylcholine receptor ( nAChRs ) subunits , and in human genetic studies , has shown the most robust association with smoking behavior and nicotine dependence to date .
 Chemical: acetylcholine; Chemical: nicotine
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: acetylcholine; Chemical: nicotine