Answer:
The correct answer is - option A. mandible.
Explanation:
Mandible is the bone of jaw especially lower jaw. It is not a bone that protects any vital organ it just help to close and open mouth for essential mouth movements like eating and talking.
Sternum and Ribs are the bones that plays role in providing protection to vital organs such as heart and lungs. Vertebral column is the bone that protects spinal chord while providing stiffness to the body and back.
Thus, the correct answer is option A. mandible.