A vein. This is because veins carry deoxygenated blood back to the heart.
Answer:
probably natural selection but it could also be discontinous variation.
Explanation:
depends on what context is??
Animalia. This is the animal kingdom, and animals do not have cell walls, only cell membranes. All other mentioned kingdoms do or might have cell walls. The lack of cell walls in animals is one of the characteristics that distinguishes which kingdom an organism belongs to.
Prokaryotes divide by a process called binary fission.