What fluid circulates around the brain and spinal cord to protect the central nervous system?

Cerebrospinal fluid is the correct answer because it plays a critical role in protecting the central nervous system, which includes the brain and spinal cord. This fluid circulates in the subarachnoid space, which is the area between the brain and the skull, as well as around the spinal cord. Its primary functions include cushioning the brain and spinal cord from trauma, maintaining intracranial pressure, and providing essential nutrients while removing waste products.

The other fluids listed do not perform the same protective functions for the central nervous system. Lymphatic fluid is primarily involved in the immune response and transportation of lymph, synovial fluid lubricates joints, and interstitial fluid serves to transport nutrients and waste between blood and tissues. None of these fluids provide the same level of protection and support specific to the central nervous system as cerebrospinal fluid does.