Could you please send me a pic or something because I think I know the answer to your question.
C.Cell wall
The correct choice is D.
A karyotype is the layout of chromosomes, in size order from largest to smallest. These chromosomes are ALWAYS in pairs, meaning that it would be easy to notice which of the 23 chromosome pairs have 3 chromosomes instead of the usual pair.
Chromosomes are pieces of tightly packed DNA that prove useful in copying DNA for mitosis.
Hope this helps :)