Answer:
B. a fixed-ratio schedule
Step-by-step explanation:
Fixed-ratio schedule: In psychology, the term "fixed-ratio schedule" is considered as one of the reinforcement schedules in operant conditioning in which a specific response is being reinforced once particular responses are being completed.
The different reinforcement schedules was proposed by one of the famous behaviorists and psychologists named B. F. Skinner.
In the question above, the given statement represents the "fixed-ratio schedule".