1990
The mean proportion of participants who reported daily smoking of crack cocaine increased from 11 . 6 % in period 1 to 39 . 7 % in period 3 .
 Chemical: crack cocaine
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Disease, Chemical 
Text: {0} 
Answer:
 Chemical: crack cocaine