Answer: Number of behavior
Explanation: Variables in an experimental research design are categorized into dependent and independent variables. Dependent variables are the measured variable in an experimental research showing variation in attribute with changes in the independent variable.
In the experiment described above, the dependent variable is the number of behaviors exhibited by the participants as they vary the independent variable, by firstly observing the problem situation of the participant, then reading them a story before presenting the problem situation and also after removal of the problem.