A schedule of reinforcement specifies which occurrences of _____________ will be reinforced.

The correct answer is behavior. A schedule of reinforcement outlines the specific conditions under which a particular behavior will be reinforced. It defines the timing and frequency of reinforcement contingent upon the desired behavior being exhibited. This can include various patterns, such as fixed-ratio, variable-ratio, fixed-interval, or variable-interval schedules, each influencing how, when, and how often reinforcement follows the behavior.

Reinforcement, though related, is not what the schedule specifies; it instead refers to the consequence that follows the behavior. Food is a type of reinforcement but does not encompass all forms of reinforcement or specify the behavior itself. Activity is a general term and does not address the behavioral component being reinforced. Thus, specifying behavior is critical for understanding how the schedule of reinforcement operates and its impact on learning and performance.