Answer:
I think the answer is C I hope you get this right, tell me if I am wrong plz
Explanation:
Let's just say that everyvyear, many people either get the vaccination, or the flu. These people are left immune to the strain of flu that they were vaccinated/infected with so the number of people who can get and pass on that form of flu (think of these people as that flu strain's "habitat") is reduced. If some of that flu mutates sufficiently that the immune systems of those previously infected vaccinated people no longer recognize it, then it's habitat is expanded back to the original size again.
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Correct answer: B. oxygen
The body is made to adapt; so it tries to adapt to its current environment. The breathing rate increases to help add more oxygen into the system, slowly boosting endurance as a survival mechanism from ages ago when we actually had to outrun predators. It was likely more efficient back then.
