<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A section from the thymus of a patient with myasthenia gravis is examined see image. The function of the portion of the thymus designated by the arrow plays what role in the pathophysiology of this disease?? A: Failure to bind MHC class II molecules, B: Failure of hematopoietic progenitor cells to differentiate in thymus, C: Premature involution of the thymus, D: Failure of afferent lymph vessels to form, E: Failure of apoptosis of negatively selected T cells,  <response>: This is a question about myasthenia gravis, which is an autoimmune disease caused by antibodies against acetylcholine receptors at the neuromuscular junction. The thymus plays an important role in the development and selection of T cells. In myasthenia gravis, there is a defect in the normal process of negative selection that eliminates self-reactive T cells in the thymus. This results in autoreactive T cells that can stimulate B cells to produce antibodies against acetylcholine receptors. Based on the image showing a section of thymus with arrow pointing to the medulla, the question is asking about the role of this region in the pathogenesis of myasthenia gravis. Choices A and B relate to normal thymic functions not directly relevant. Choice C refers to age-related involution which is not the primary pathology. Choices D and E relate to defects in T cell selection, with E being the failure of apoptosis of autoreactive T cells that escapes negative selection.E: Failure of apoptosis of negatively selected T cells 