The answer is letter D.
A group of white blood cells that has of small and large lymphocytes.
The small lymphocytes bear variable cell-surface receptors for antigen and are
responsible for adaptive immune responses. There are two main group of small
lymphocyte—B lymphocytes (B cells) and T lymphocytes (T cells). Large granular
lymphocytes are natural killer (NK) cells, lymphocytes of innate immunity.
