Which of the following is not a type of adaptation?

I'm not exactly sure but i have a feeling it is c. is not an adaptation

Here is my reasoning. Remember adaptation is a result of natural selection and natural selection is based on the environment.

A. If the function has a purpose for the environment, it will survive. For example, we managed to have eyes because it serves a purpose of seeing our environment. Compared to fish eyes, we see a lot less of our environment but we have sharp clear vision for nearby objects. Even bees can see in ultraviolet to detect pollen or something like that. Don't quote me on the bee thing. If you're interested, check out how animals see the word on youtube. It'll make much more sense.

B. Structural adaptation coexist with function. Think of birds. There are so many beaks with different shapes and such. They are different structure because they have different function.

C. I can't think of any mechanical adaptation. If you can think of any reason you might consider this choice, tell me and I'll see if I can explain why c. is not an adaptation

Clean air provides nitrogen