Most the bones in our body are made of the same materials. Each bone has four main layers. The outside of the bone is called the periosteum. This layer contains nerves and blood vessels that bring nutrients to the bone. Next is the compact bone. It is the hardest part of the bone. Inside the compact bone is the cancellous bone. This part of the bone is light and spongy, but still strong. The innermost layer of bone is called the marrow. This layer is almost like a thick jelly. Bone marrow produces red blood cells, which help to bring oxygen to all the different parts of our body, and white blood cells, which our body uses to fight off diseases and infections. Our skeleton also gives our body its shape and allows us to move. The skeleton is our body’s frame; if we did not have bones, we would all flop around like jellyfish. The special way our bones connect enable movement. The places where our bones meet are called joints. These are the parts of your body that you can bend and move, like your knees, elbows, shoulders, and fingers. For an example, look at one of the legs on the diagram of the skeleton. You will see bones called the femur, the tibia, and the fibula. The place where these bones meet is the knee. The knee is a joint; it is protected by the patella bone (also called the kneecap).

Finally, our bones also protect our most important organs. As you might imagine, bones are much harder than the soft, fragile organs inside of our body. For example, the ribs and sternum protect our heart, lungs, and major blood vessels. The skull protects our brain. The vertebrae in our spine protect the nerves in our spinal column. Without our bones, our bodies’ most vital organs would be much more vulnerable.

The next time you see a skeleton while watching a scary movie or visiting a haunted house, remember: those bones may be creepy, but you would not be able to live without them!
According to the passage, all of the following are protected by a bone EXCEPT

A
the stomach

B
major blood vessels

C
the brain

D
the knee joint