Final answer:
Double-negative CD3- thymocytes are mismatched with the cortico-medullary junction in the thymus during T cell development and differentiation.
Step-by-step explanation:
In the thymus, T cells go through a process of development and differentiation. Thymocytes that do not bear the CD4 or CD8 molecules are referred to as double-negative. During this stage, in the cortex of the thymus, the double-negative thymocytes are exposed to cortical epithelial cells. This is called positive selection, where they bind to self MHC molecules. The correct answer is option a: double-negative CD3- thymocytes are mismatched with the cortico-medullary junction.