"mason, a stockbroker, runs two miles every day after work because it reduces his level of stress. mason's running habit is maintained by a reinforcer."

The correct answer is the negative reinforcer. Negative reinforcement is defined as a theory of operant conditioning by which the response or behavior is being strengthened by which it involves with having to remove, stop, or avoid a certain outcome.

answer; the parasympathetic nervous system;

answer; humanistic;