Given a scientific question, generate a correct answer to it.

Example Input: Slow-twitch or fast-twitch and oxidative or glycolytic describe what type of fibers?
Example Output: skeletal muscle fibers

Example Input: In vertebrates, a system of what structures attached to the endoskeleton enables movement?
Example Output: muscles

Example Input: What is the tissue beneath a mollusks' shell called?
Example Output:
mantle