Myasthenia gravis is an autoimmune disorder in which

a. myelin sheath is destroyed.
b. the neurotransmitter is destroyed.
c. the neurotransmitter receptors of gland cells are destroyed.
d. the neurostransmitter receptors of muscle fibers are destroyed.
e. synaptic clefts are filled in.

d. the neurostransmitter receptors of muscle fibers are destroyed.