Dr.Santiago is investigating the effect of warm room temperature on aggressive behaviour in preschoolers.Half of the children are in a classroom where the temperature is 31°C (hot) and half are in a classroom where the temperature is 21°C (normal) .Dr.Santiago measures the number of hitting incidents that occur in each classroom.In this study,what is the term for the number of hitting incidents

A)  control group
B)  experimental group 
C)  independent variable
D)  dependent variable