Question

the yolk sac ____________. a is the first site of blood cell formation b forms the fetal half of the placenta c becomes the umbilical cord vessels d provides nutrition until the placenta is formed

Explanation:

• The yolk sac is indeed the first site of blood cell formation in the embryo.
• The fetal half of the placenta is formed by the chorion frondosum.
• The umbilical cord vessels develop from the allantois.
• The yolk sac does not provide nutrition until the placenta is formed; in humans, the yolk sac is vestigial in terms of nutrition - providing function (in contrast to some other animals).

Answer:

A. is the first site of blood cell formation