DrSherman Is Working in a Clinic with Children with Developmental

Dr.Sherman is working in a clinic with children with developmental delays and decides to implement a new program to encourage more positive behaviour.Whenever children engage in specific behaviour (such as saying,"Thank you," taking turns with a friend,and cooperating with another child on a project) ,they are rewarded with stickers that can later be turned in for various prizes that they enjoy.Dr.Sherman is using which of the following therapeutic techniques?

A) higher order classical conditioning
B) modeling
C) negative reinforcement
D) a token economy
E) unconditional positive regard