The formation of blood cells is a complex process. in most cases, the cells have been transformed ("morphed") from a previous cell type. the precursor cells from which each individual type of blood cell is formed through a series of maturation steps are called
stem cells
progenitor cells
colony-forming units
blast cells
all of these choices

The correct option is: (A) stem cells

Explanation:

The bone marrow is a semi-solid tissue which is generally found in the spongy portions of the bones. In the bone marrow, all the blood cells are produced from the unspecialized precursor cells, which are known as the stem cells. Firstly, the stem cells divide and form the immature blood cells. These immature blood cells then further divide and mature to form the mature blood cells.

Therefore, the stem cells are the precursor cells which transform and mature to form the blood cells.

oceans

indian ocean

pacific ocean

atlantic ocean

arctic ocean

southern ocean