Final answer:
The lumbar vertebrae are not part of the rib cage, which consists of the sternum, thoracic vertebrae, ribs, and costal cartilages. The correct option is A.
Step-by-step explanation:
The question asks which structure is not part of a person's rib cage. The rib cage consists of the ribs, sternum, thoracic vertebrae, and costal cartilages. Option A, the lumbar vertebrae, is not part of the rib cage.
The thoracic cage, also known as the rib cage, encloses and protects the vital organs in the thoracic cavity such as the heart and lungs, and provides structural support and attachment points for muscles.
The thoracic cage is made up of the sternum at the front, the ribs which are connected to the thoracic vertebrae at the back, and the costal cartilages which attach the ribs to the sternum. However, the lumbar vertebrae are found below the thoracic region and they support the lower back, not being part of the rib cage. Option A. is the correct one.