I think the correct answer would be A. The yolk sac becomes the placenta. It is membranous sac that is attached to the embryo. It provides all the nutrition and the blood cells needed by the embryo. It is also called the umbilical vesicle.
This is a new gibbous moon.
The sun. Greenhouse gases absorb heat better. So the more of these gases, the hotter it gets. However, the earth itself is naturally heating, but it goes too fast for live to adjust to the temperatures.
Answer:
The human skeleton performs six major functions: support, movement, protection, production of blood cells, storage of minerals, and endocrine regulation
