A boy was riding a horse for the first time. The horse ran more quickly than he expected, and he fell off, hitting his head on a rock. A doctor’s exam revealed that he was okay, except for a few scrapes. What protected his brain from injury?

his spine, which lines the vertebral cavity

his skull, which encloses the cranial cavity

his abdominal cavity, which is filled with liquid

his spinal cord, which sends the brain messages