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 answer is D. For producing recombinant, first you need to cut the insert part and vector part to get the same end by using restriction enzyme. Then using DNA ligase to bind these two parts to get a new plasmids.
These are called sunspots, and appear regularly. They are cooler than the rest of the Sun's surface because of the extremely strong magnetic fields inside of them.
D is the ion found in water
I think A) but not really a lot of info
