Final answer:
CD stands for Cluster of Differentiation, which are markers used to identify various types of white blood cells like T cells, with CD4 and CD8 being the most important for T cell differentiation. Option 2) is correct.
Step-by-step explanation:
The term CD in the context of Cluster of Differentiation stands for Cluster of Differentiation, not Cell Differentiation, Cell Division, or Cell Death. Cluster of Differentiation molecules are cell surface glycoproteins that are crucial in the immune system for identifying and distinguishing between different types of white blood cells. More specifically, CD4 and CD8 are two critical CD molecules associated with T cells; CD4 is expressed on the surface of Helper T cells and regulatory T cells, whereas CD8 is expressed on cytotoxic T cells.
Cell differentiation is a separate process wherein cells become specialized to assume unique structures and functions during the development of an organism. Stem cells are at the heart of this process. They have the ability to divide indefinitely and, under certain conditions, can differentiate into a variety of specialized cells. Differentiation involves the cell reading only specific parts of DNA relevant to its function, similar to actors only reading their parts from a movie script.