Membranes that surround the brain and spinal cord are called a. hydrocephali b. ventricles c. csf d. meninges

The correct answer is "meninges"

Meninges are the membranes composed of three layers, from external to internal, the dura mater (alone called the pachymeninx), the arachnoid mater, and the pia mater (together called the leptomeninx). Meninges serve to protect the brain by establishing the blood brain barrier.

Alright, i'm gonna try to explain this as good as possible. the law of conservation is like a collection overtime. it never changes though. no matter how you change the constituent parts.