Name the following.
The fluid that fills the cavities in the brain and spinal cord

Explanation

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks for the name of the fluid that fills the cavities in the brain and spinal cord.

2. **Recall Relevant Information**: In biology, it is known that there is a specific fluid that serves this purpose in the central nervous system.

3. **Name the Fluid**: The fluid that fills the cavities in the brain and spinal cord is called **cerebrospinal fluid**.

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