During the process of muscle contraction, the sarcoplasmic reticulum is stimulated to release which substance?

Rationale:
A. Red blood cells are primarily produced in red bone marrow, not yellow bone marrow. Red marrow is found mainly in flat bones (such as the pelvis, sternum, and ribs) and is the primary site of hematopoiesis (formation of blood cells).
B. Yellow bone marrow is made up largely of adipocytes (fat cells). Its main function is fat storage, which serves as an energy reserve. In adults, much of the red marrow gradually converts into yellow marrow with age, especially in the long bones.
C. Like red blood cells, most white blood cells are formed in red bone marrow, not yellow marrow. While yellow marrow can, under extreme conditions (such as severe blood loss), revert to red marrow to aid in hematopoiesis, its normal composition is primarily fat.
D. Cartilage is a connective tissue found in joints, the rib cage, ear, nose, and other structures. It is not a component of bone marrow.

Rationale:
A. Flexion decreases the angle of a joint, such as bending the elbow or knee, but it does not describe spinning away from the midline.
B. Internal Rotation involves turning a bone toward the body’s midline.
C. Abduction is the movement of a limb away from the body’s midline, such as raising the arm or leg outward. This matches the definition in the question.
D. External Rotation is the spinning of a bone around its axis away from the midline, but the question specifically refers to movement away, not rotation.