Lester, a 29-year-old smoker, has a head injury and lives in a group home with four other men They have staff members who are with them 24 hours per day to help them with everyday tasks. Lester often displays aggressive or otherwise inappropriate behaviors as a result of his brain injury. For this reason, the staff members have been trained by the agency psychologist to give him a coupon every time Lester shows an appropriate behavior. When he saves up eight coupons, Lester is rewarded with a cigarette. Which of the following techniques is the staff members using with Lester?a) healing circleb) aversion therapyc) a token economyd) unconditional positive regard