James was exposed to a pathogen when he was 10 years old and felt ill. What would most likely happen if he were exposed to the same pathogen when he is 12 years old? His body would destroy the pathogen before he felt symptoms. His reaction to the pathogen would be worse than the first. His antibodies would decrease, since he had been exposed already. New types of antibodies would be made in response to the second exposure.

A. Write the letter for the correct answer. \( \begin{array}{lll}\text { 1. The muscular system has } & \\ \begin{array}{lll}\text { (a) two } & \text { (b) three } & \text { (c) ten }\end{array} \\ \text { 2. Muscles are made of muscles. } \\ \begin{array}{lll}\text { (a) cells } & \text { (b) tendons } & \text { (c) ligaments }\end{array}\end{array} \).

4. The skull protects the brain. 5. The ribs protect the spinal cord. 6. The ribs are part of the skeletal system.

Answer True or False. 1. Cartilage is harder than bone. 2. You have the same amount of cartilage in your body all your life. 3. Bones can repair themselves. 4. Red blood cells are made in marrow. 5. Bones always stay the same size. 6. Some cartilage changes to bone.

The part of the skeleton that protects the spinal cord is the \( \begin{array}{lll}\text { (a) rib cage } & \text { (b) skull } & \text { (c) backbone } \\ \text { The } & \text { is the part of the skeleton that protects the heart. } \\ \begin{array}{lll}\text { (a) skull } & \text { (b) rib cage } & \text { (c) backbone }\end{array}\end{array} \)

Use each word to write a sentence about how your body moves. 1. hinge joint 2. ball-and-socket joint