Which of the following is a primary function of the skeletal system?

• A. Producing blood cells
• B. Regulating body temperature
• C. Storing vitamins
• D. Filtering waste from blood

Answer: (A)

The essential idea here is that the skeletal system is a cradle for blood formation. Red bone marrow inside many bones continuously makes blood cells—red cells to carry oxygen, white cells to fight infection, and platelets to help clotting. This process, hematopoiesis, is a defining, ongoing function of the skeletal system and why producing blood cells is the best choice among the options.

The other options point to roles outside the bone’s main job: regulating body temperature is mainly a function of the skin and metabolic processes; filtering waste is handled by organs like the kidneys and liver; while bones do store minerals, storing vitamins isn’t a primary skeletal function.