Answer:
C. tokens are exchanged for valued reinforcers to increase the frequency of a desired behavior.
Step-by-step explanation:
In Token economy, the token could be anything that is considered as a reward.
For examples,
Let's say that you have a son.
In Order to encourage your son to make more effort on his test, you told him that you will give him one gold sticker every time he get B+ or higher on his tests. If he get 3 stars, he can exchange it with a box of ice cream of his choosing.
From the example of a token economy above, the gold stars acted as a token that reinforce the son's behavior. Since the son desire it so much, he will more likely to make more effort in studying, which is a desired behavior that the you want to impose to the son