veins carry deoxygenated blood back to the heart.
Answer:
Population
Explanation:
An Organism would be 1 single mouse, a community encompasses multiple animals living in that same area, a niche has to do with where they are living and how they interact, so only the population makes sense.
Its B ( at 4 degrees) as at this temp 2 opposite effects are in balance
They are movement, homeostasis, and energy.