The Major Difference Between Gram-Positive and Gram-Negative Bacteria Is That

The major difference between gram-positive and gram-negative bacteria is that:

A) the peptidoglycan layer in gram-positive bacteria is substantially thinner than in gram-negative bacteria.
B) gram-positive bacteria contain a periplasmic space,whereas gram-negative bacteria do not.
C) flagella are only present in gram-positive bacteria.
D) gram-negative bacteria contain an outer membrane that functions as the cell's initial barrier to the environment.