Which statement about the muscular system is true?

• A. It affects posture, joint stability and heat production.
• B. It is the primary site of oxygen transport in the blood.
• C. It filters wastes from the body.
• D. It stores calcium for the bones.

Answer: (A)

Muscles maintain posture, stabilize joints, and generate heat through contraction, especially the constant work of postural muscles and the heat produced during activity or shivering. This is why the statement is true: the muscular system directly influences posture, helps keep joints stable during movement, and is a major source of body heat. The other functions don’t belong to muscle tissue: oxygen transport is carried by red blood cells in the blood, waste filtration is done by organs like the kidneys and liver, and calcium storage is primarily in bones (muscles use calcium for contraction but do not serve as the body's main calcium reservoir).