【单选题】Which one of the following is the most accurate description of the structural differences between gram-positive bacteria and gram-negative bacteria ?
A.
gram-positive bacteria have a thick peptidoglycan layer, whereas gram-negative bacteria have a thin layer
B.
gram-positive bacteria have an outer lipid-rich membrane, whereas gram-negative bacteria do not
C.
gram-positive bacteria form a sex pilus that mediates conjugation ,whereas gram-negative bacteria do not
D.
gram-positive bacteria have plasmids, whereas gram-negative bacteria do not
E.
gram-positive bacteria have capsules, whereas gram-negative bacteria do not