As part of an experiment on the effects of behavior modeling, a set of raters are evaluating the prosocial behavior in a three hour recording in a class of preschoolers. During the first hour (9- 10am), baseline prosocial behavior is coded for each child. During the second hour (10-11am), the teachers model prosocial behavior. During the third hour (11-12pm), prosocial behavior is again coded for each child. The researchers found a decrease in the prosocial behaviors. They wonder if the children might have been acting less prosocially due to fatigue or hunger. Which threat to internal validity are they worried about? a) attrition
b) maturation
c) history
d) testing