Which stage is the last stage of speciation?

The populations become adapted to different environments and eventually become so different that they cannot imterbreed to produce fertile of spring.

Speciation is the evolution of one species into two different kinds , and when they become isolated , that is the final step , since they cannot interbreed any longer .

Explanation:

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a. decomposes use carbon from dead organisms as fuel for cellular respiration, returning carbon dioxide back into the atmosphere.

trachea, alveoli, lung capillaries, arteries