This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
Which of the following steps involved in formation of CSF? 
Select and explain. 
A. Ultrafiltration and active secretion, B. Passive secretion, C. Active secretion and passive filtration, D. None
A: Ultrafiltration and active secretion
Answer: A: Ultrafiltration and active secretion 
Explanation: Ultrafiltration through fenestrated capillary walls Active secretion of ions and solutes Ref gk pal pg no 1157