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