This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nerve, Subject name: Physiology
True about Wallerian degeneration 
Select and explain. 
A. It is proximal degeneration, B. Myelin sheath degeneration is the first change to occur, C. It's a type of nerve regeneration, D. None
D: None
Answer: D: None 
Explanation: Distal (Wallerian) degeneration: mediated by calcium influx and activation of axonal proteases 24 hours:neurofilaments break up and the axon fragments into sho lengths. Within 10 days:myelin decomposes into fat droplets (after 10 days, Schwann cells begins to fragment myelin sheath.....a change from myelinating to demyelinating) In 3 months: macrophages phagocytose the debris, leaving behind only endoneural tube/ ghost tube (filled by the rapidly multiplying Schwann cell's cytoplasm)