Cerebrospinal fluid is formed from blood by clusters of capilaries in the brain As choroid plexuses B) Arachnoid villi C) ventricles D) sinuses

1. **Understanding the Question** The question asks which structure in the brain forms cerebrospinal fluid (CSF) from blood by clusters of capillaries. 2. **Identifying the Structure** The specialized network of capillaries within the brain that filters blood and produces CSF is known as the \( \textbf{choroid plexus} \). 3. **Explanation** The choroid plexuses are located within the ventricles of the brain and consist of a layer of specialized ependymal cells surrounding a core of capillaries. These cells actively filter substances from the blood to produce CSF. Other structures mentioned, like arachnoid villi, ventricles, and sinuses, have different functions: - The arachnoid villi are responsible for the reabsorption of CSF into the blood. - The ventricles are cavities that contain the CSF. - The sinuses are channels that help drain blood. 4. **Conclusion** Since the CSF is formed by the capillaries within the choroid plexus, the correct answer is: **A) Choroid plexuses.**