Final answer:
The group leader is engaging in progressive relaxation training.
Step-by-step explanation:
The best answer is b. Progressive relaxation training. In the given scenario, the group leader is guiding the patients to focus on their breathing and then to focus on specific body parts, such as the left arm. This technique is known as progressive relaxation, which involves systematically tensing and then relaxing different muscle groups to induce deep relaxation and reduce stress.