The correct option is
A Loss of cell-mediated immunity
Lymphoid organs are the organs where origin and/or maturation and proliferation of lymphocytes occur.
The thymus is a flat, bilobed lymphoid organ situated above the heart beneath the breast bone. Each lobe is divided into two compartments namely the cortex and the medulla. The cortex is the outer compartment while the medulla is the inner compartment.
Thymus is large in size at the time of birth and starts decreasing in size after puberty. It helps in the maturation and selection of T-lymphocytes by providing them with the proper micro-environment.
Since T-lymphocytes are the major effectors of cell-mediated immunity, any damage to it may lead to loss of cell-mediated immunity. Hence option a is correct.
Figure : A - Location of thymus in the body, B - Structure of thymus
Stem cells are cells with the potential to develop into different types of cells in the body. Examples include hematopoietic stem cells in bone marrow. Thymus does not produce stem cells. Hence option b is incorrect.
Antibody-mediated immunity is associated with bone marrow, which produces B cells. So option c is incorrect.
Hemoglobin develops in cells in the bone marrow. So option d is incorrect.