I think the answer should be medulla oblongata or foramen magnum.
The major nerves that leave brain should form a thick cord in the brain stem that called medulla oblongata. Medulla oblongata will pass a big hole in the base of the skull that called foramen magnum. Depends on what part the question asked(bone or tissue), it probably between those two options.
Answer:
B: an atom
Explanation:
An atom is the smallest substance that can exist in isolation.
Hence, if a piece of copper is continually divided, eventually the smallest particle you would get in an atom.