Given a scientific question, generate an incorrect answer to the given question. The incorrect answer should be a plausible alternative to the correct answer. The answer should be some other item belonging to the same category as the correct answer but should be incorrect.

[Q]: Organic compounds are molecules built around what element?
[A]: helium

[Q]: In vertebrates, a system of what structures attached to the endoskeleton enables movement?
[A]: nerves

[Q]: Cycling, shoveling snow and cross-country skiing are examples of what kind of heart-strengthening activity?
[A]:
metabolism