I’m pretty sure the answer is c
Answer: D. Extinctions occur at higher rates during times of ecological stress when populations and species are poorly adapted.
Answer:
The return of blood to the heart is assisted by the action of the skeletal- muscle pump. As muscles move, they squeeze the veins running through them. Veins contain a series of one-way valves, and they are squeezed, blood is pushed through the valves, which then close to prevent backflow.
after the evolution of the first living cells, fermentation wasn't needed, because aerobic respiration was now doable, since there was more oxygen in the air now. also, as the temperature increases, it becomes more energy consuming to conduct fermentation over aerobic respiration.
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