Final answer:
The brain is housed in the cranial cavity, which is a part of the dorsal cavity, located at the posterior of the body and protected by the cranial bones and cerebrospinal fluid.
Step-by-step explanation:
The body cavity where the brain is situated is known as the cranial cavity. This cavity is part of the dorsal cavity, which also includes the spinal cavity or vertebral cavity. The dorsal cavity is at the posterior of the body and protects the brain and spinal cord with the bones of the skull and vertebral column along with cerebrospinal fluid. Thus, the correct answer to the question is the cranial cavity, not the pelvic, vertebral, or thoracic cavities.