The is the site of the which is the first site of hematopoiesis in the developing embryo.
a. cardiogenic mesoderm, liver
b. bone marrow, blood islands
c. ectoderm, blood islands
d. yolk sac, blood islands

D

Explanation:

During embryogenesis, hematopoiesis begins in week 3 in the Yolk Sac, in Pander´s Island or Wolff´s Island, commonly known as the "blood islands". These blood islands develop from the umbilical vesicle, allantois, and chorion. In week 5, blood production starts on the fetal liver, and finally, at week 12 it begins in the bone marrow, spleen and, thymus.

i dont know it at allnow im just getting points at this pint

geologic time scale (for gradpoint) =)