The correct answer is (d), embryonic stem cell. Embryonic stem cells are pluripotent, meaning they can differentiate into any type of cell in the body. They are derived from the inner cell mass of a blastocyst, which is a stage of embryonic development that occurs about 5 days after fertilization.
Progenitor cells are also stem cells, but they are more limited in their ability to differentiate. They can only give rise to a certain type of cell or group of cells. For example, hematopoietic stem cells can give rise to all types of blood cells.
Megakaryocytes are not stem cells. They are large cells in the bone marrow that produce platelets, which are blood cells that help to stop bleeding.
Adult stem cells are stem cells that are found in adult tissues. They are less pluripotent than embryonic stem cells, but they can still differentiate into a number of different cell types. For example, mesenchymal stem cells can give rise to bone, cartilage, and fat cells.