To establish a neutral stimulus like praise as a conditioned reinforcer it must be consistently paired with an already established unconditioned or powerful conditioned reinforcer in this case strawberries This process is known as stimulusstimulus pairing or conditioning through association By repeatedly delivering praise immediately before or simultaneously with a highly preferred item like strawberries praise will acquire some of the reinforcing properties of strawberries Over time praise alone may begin to function as a reinforcer Option A token economy is a complex system and while tokens become conditioned reinforcers simply exchanging for praise which isnt a reinforcer yet wouldnt work If tokens were exchanged for strawberries it could work but the question is specifically about establishing praise as a reinforcer directly Option B changing criterion design is unsuitable for establishing new reinforcers or skills its for shaping an existing behavior Option D functional assessment would be relevant if Peters nonresponsiveness to praise was a problem behavior but the goal here is to establish praise as a reinforcer not to analyze the function of its current ineffectiveness which is already known its not reinforcing