The skeletal system has a variety of functions, including protecting internal organs, storing minerals and energy molecules, and assisting in movement.

The production of heat, however, is a function of the muscular system.

Red bone marrow is found in the epiphyses, or ends of long bones. It is the site of hematopoiesis, or red blood cell development.

Yellow bone marrow is primarily composed of fat. Osteons are the functional units of bone, and house the cells that build and break down the bony matrix. Cartilage is found on the articular surfaces of bone, and helps provide support for joints.

Bone marrow is the major producer of blood cells, including most of those in the immune system.

The other answer options listed are functions of the bones in the skeletal system, but are not directly linked to the bone marrow. The skeletal system stores calcium and phosphorus, which in turn make the bones strong. Bones can complement to liver to detoxify blood by removing metals such as lead and radium. Muscles attach to bones and generate movement. The skull protects the brain. The rib cage protects the heart and lungs. 

Ligaments are made of dense connective tissue and connect bone to bone. Have you ever sprained your ankle? Chances are you partially or fully tore some ligaments in your ankle. Unfortunately, ligaments do not heal very well since there is almost no blood supply to them, and instead lay down scar tissue. Tendons connect bone to muscle. Muscles are already attached to tendons.

Osteoclasts are cells that resorb, or destroy bone, and are found in lacunae of bones. Since one of the functions of bone is storage of minerals, if the mineral content of the blood drops below the set point, osteoclasts are recruited. They break down bone, releasing the minerals into the blood. Osteoblasts do the opposite. If the levels of minerals in the blood are higher than the set point, osteoblasts will take them and convert them into bone via a process called bone formation, or ossification. 

There are actually only three types of bone cells: osteocytes, osteoclasts, and osteoblasts.  Osteoblasts are the "builders" (think "blasts build") and are responsible for laying down new bone for the constant bone remodeling that goes on throughout all your life as well as initial bone growth. Osteoclasts are the opposite of osteoblasts and are also active in bone remodeling by taking old bone away (think "clasts kill"). Osteocytes are the third and final type that are inactive and are found in individual lacunae (think "cytes sit"). Chondrocytes are cartilage cells. 

Osteoclasts break bone and cause calcium to be reabsorbed into the blood stream whereas osteoblasts lay foundations for new bone mineralization. 

During muscle contraction, the muscle deemed the agonist will contract while the antagonist will stretch. The agonist will cause the primary action and the antagonist would cause an opposite action. Synergists assist the agonist by stabilizing the origin bone, which facilitates movements and posture.

For example, the biceps brachii (agonist) is used to flex the arm, while the triceps brachii (antagonist) is used to straighten the arm. The brachialis is also used to flex the arm, but in a different way, making it a synergist to the biceps brachii.

Tendons are separate from muscle, and are used to secure a muscle attachment to bone.

No chemical digestion occurs in the esophagus. The esophagus is used in order to move food into the stomach using peristaltic motion.

Amylase is introduced in the mouth and begins breaking down carbohydrates. Pepsin in the stomach helps digest proteins. Lipase, trypsin, and other digestive enzymes are introduced in the small intestine, where the majority of chemical digestion takes place.

The duodenum is the first section of the small intestine. It is the site of the most digestion in the small intestine (and the digestive tract in general) because pancreatic enzymes and bile are released into its lumen. These enzymes break down proteins and carbohydrates, while the bile helps to digest lipids and fats. The jejunum and ileum are primarily involved in absorbing nutrients. The cecum is part of the large intestine.