Final answer:
The correct answer is B.The pectoralis major muscle is involved in adducting the humerus, bringing the arm toward the body's midline.
Step-by-step explanation:
The pectoralis major muscle is responsible for several movements of the humerus, the long bone of the arm.
Specifically, it participates in adducting the humerus, which means it helps to bring the arm toward the body's midline. The pectoralis major is a thick, fan-shaped muscle located on the superior portion .
The anterior thorax and originates from the sternum and clavicle. It inserts into the humerus bone and plays a crucial role in the arm's movements.
Therefore, the correct answer to the student's question is b. adducting the humerus. This action is contrasted with the latissimus dorsi muscle, which helps in extending the arm inferiorly.
It is different from the muscles involved in the retraction of the scapula or the rotation of the radius, which are not primarily functions of the pectoralis major.