Im thinking its D. bcuz all three A. B. C. are true
The scheme of modern taxonomy goes:
Life > Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species
So, a PHYLUM is made of several classes.
The answer to the given question (though the question isn't given), I can assume this is the same as a previous one as the answer is C.
Hope this helped!
If you're talking about eukaryotic cells then it's the cell wall. If it's a prokaryotic cell sometimes the slime layer secreted by some bacteria may harden and form a capsule around the bacterial cell.
Hope i helped!