At Skinner Elementary School, Teachers Pass Out "Skinner Bucks" to Students

At Skinner Elementary School, teachers pass out "skinner bucks" to students who turn in papers on time, obey the teacher, and finish their homework. The paper "bucks" can be traded in at the end of the week for special treats or game-playing time on the classroom computer. This system most resembles a

A) participant modeling technique.
B) contingency contract.
C) group extinction procedure.
D) token economy.
E) Thorndike technique.