This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
The anti- acetylcholine receptor (AChR) antibodies in myasthenia gravis reduce the number of available AChRs at neuromuscular junctions with which of the following mechanism ? 
Select and explain. 
A. accelerated turnover of AChRs, B. damage to the postsynaptic muscle membrane, C. blockade of the active site of the AChR, D. all of the above
D: all of the above
Answer: D: all of the above 
Explanation: The anti-AChR antibodies reduce the number of available AChRs at NMJs by three distinct mechanisms: (1) accelerated turnover of AChRs by a mechanism involving cross-linking and rapid endocytosis of the receptors; (2) damage to the postsynaptic muscle membrane by the antibody in collaboration with complement; and (3) blockade of the active site of the AChR. Ref harrison 20th edition page 3232