The correct answer is a) mitosis.
Stem cells are unique in their ability to both self-renew and differentiate into various cell types. This self-renewal occurs primarily through the process of mitosis, which is a type of cell division that results in two genetically identical daughter cells. In contrast, meiosis is a different process that creates gametes (sperm and eggs) and is not involved in stem cell proliferation.
Differentiation refers to the process by which stem cells become specialized cells, which is not the same as generating more stem cells. Fertilization is the union of sperm and egg, irrelevant to stem cell division. Thus, while stem cells can differentiate into other cell types, they primarily produce more stem cells through mitosis.