The many different cell types in the blood of an adult mammal are derived from
选项：

A:a single type of multipotent stem cell found in the bone marrow;
B:differentiated cells that first developed in the fetal liver, but now reside in the bone marrow;
C:division of differentiated cell types while circulating in the blood;
D:stem cells that became committed to each specific blood celll type during embryonic development