The bronchi are where air passes from the trachea.
Answer:
a- black powder
Explanation:
it is powder and has no pigment
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.
The place where these molecules fit is called the active site .