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.
A. soldis
I thinks it‘s A. DNA
D. Columnar
Hint the root word is in the option and it is actually shaped like a column according to Epithelium - Wikipedia
Hope this helps : )