Which One of the Following Illustrates All the Necessary Elements

Which one of the following illustrates all the necessary elements of a contingency contract?

A) Mr.Osaka wants to reduce Penny's aggressive behaviors toward her classmates.He and Penny meet and discuss the problem, agreeing on the specific behaviors she should demonstrate and the reinforcers she will receive when she does so.They both sign a contract that describes the desired behaviors and the reinforcement.
B) Ms.Quineras wants Ramon to learn to stay in his seat and complete his assignments during independent seatwork time.She makes up a contract for Ramon that describes the consequence he can expect if he does not behave appropriately.They both sign it, and she follows through with the consequence when he misbehaves.
C) Mr.Sellers wants to help Trina learn to complete her homework in a more timely fashion.He has Trina write up a contract stating that she will complete her homework on time and specifying the reinforcer she would like to receive each time she does so.Both teacher and student sign the contract, and Mr.Sellers reinforces Trina as she has requested.
D) Mr.Enright develops a contract for her fifth graders that lists several classroom rules the students must agree to abide by.Each student signs the contract, thereby