Explanation:

The correct answer is 'behavior modification.' The Token Economy is a form of behavior modification that involves providing positive reinforcement in the form of tokens or rewards for desired behaviors. This approach aims to increase the occurrence of positive behaviors by rewarding them. Play therapy (choice A) focuses on using play as a medium for therapeutic communication, not specifically behavior modification. Milieu therapy (choice C) involves shaping the environment to promote desired behaviors but is not the primary focus of the Token Economy. 'Associative' (choice D) is not directly related to the Token Economy or its focus on behavior modification, making it an incorrect choice.