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.

the answer is c.) there is a warm front in region a and a stationary front in region b.

hey, i believe your answer would be d. sugar ribose and the base uracil. i believe this is the answer, because rna consists of sugar ribose, adenine, guanine, cytosine, and uracil.

your first option is incorrect, because that's dna. where it consists of sugar deoxyribose, adenine, guanine, cytosine and thymine.

your second option is also incorrect, this is because sugar deoxyribose is in dna, and uracil is in rna. these two do not make sense together.

your third option being incorrect, because sugar ribose is in rna, but not the base of thymine. rna consists of uracil, not thymine.

lastly your fourth option being correct! this answer is correct, because both sugar ribose, and the base uracil are in rna! ~

answer is d. sugar ribose and the base uracil.