Final answer:
The muscles responsible for downward rotation of the scapula are the levator scapulae, pectoralis minor, and rhomboids.
Step-by-step explanation:
The muscle groups that act to produce downward rotation of the scapula include the levator scapulae, pectoralis minor, and the rhomboids. The levator scapulae elevates the scapula but also helps with downward rotation when the scapula is elevated. The pectoralis minor assists in rotating the scapula downward by drawing the scapula anteriorly and inferiorly. The rhomboids (major and minor) also play a role in downward rotation by pulling the scapula medially. Thus, the correct answer to the question is option D: Levator scapulae, pectoralis minor, and rhomboids.