Final answer:
Rachel's boss congratulating her for each new client acquisition is an example of a fixed ratio schedule of reinforcement, which is a form of positive reinforcement.
Step-by-step explanation:
Rachel's boss sends congratulations each time she acquires a new client, providing a reward after a set number of responses (acquiring new clients). This consistent reinforcement after a specific number of desired behaviors is an example of a fixed ratio schedule of reinforcement. With this schedule, positive behavior is rewarded after a consistent number of responses, which in this case is the acquisition of a new client. It reflects a system aimed at increasing the quantity of output, like Carla's commissions in the eyeglass store scenario provided. It is not dependent on a set amount of time, as with a fixed interval schedule, nor is it unpredictable like a variable ratio or variable interval schedule.
Therefore, the answer to the question is: B. positive reinforcement, and more specifically A. a fixed ratio schedule of reinforcement.