1811
Half of the offspring in each of the four resulting groups / gender were exposed to positively reinforced ( food - rewarded Fixed Interval schedule - controlled behavior ) or negatively reinforced ( inescapable forced swim ) BE .
 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