Warm blooded animal maintain their temperatures at a constant.When it is cold they generate heat to keep themselves warn,they also try to cool themselves when it is cold. This animals include Human-beings and Dogs
It is called a double circulatory system because blood passes through the heart twice per circuit. The right pump sends deoxygenated blood to the lungs where it becomes oxygenated and returns back to the heart.
Answer:
it's the last one, everything else would be an increase in the population
