This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Which of the following glial cells helps in myelination of CNS neurons? 
Select and explain. 
A. Astrocytes, B. Schwann cells, C. Microglial cells, D. Oligodendrocytes
D: Oligodendrocytes
Answer: D: Oligodendrocytes 
Explanation: None