Answer: Option D.
Whether their cell walls have a thin or thick layer of peptidoglycan.
Step-by-step explanation:
Gram positive bacteria have thick cell wall layer of peptidoglycan and their cells stain purple when subjected to gram staining which is crystal violet. Examples are anthrax bacteria, diphtheria e.t.c.
Gram negative bacteria have thin cell wall layer of peptidoglycan and tend to retain the color when stained with crystal violet or gram staining. Examples are E.coli, pseudomonas aeruginosa e.t.c. Gram staining is important to differentiate between gram positive from gram negative bacteria.