The best answer is D, birds.
For more information and details on the way a bird's respiratory system works:
https://asknature.org/strategy/air-flow-patterns-facilitate-efficient-gas-exchange/
Answer:
substantive genes
Explanation:
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D. A struggle for existence is apparent.
If a struggle for existence is apparent, natural selection occurs because all of the weak/unfit/unadapted ones die.
Can you list options since its which of the following?
