What feature of mycobacteria is responsible for the unusually slow growth of these bacteria?

A) Their low tolerance for oxygen retards their growth.
B) They cannot fully metabolize carbohydrates and must rely on fermentation.
C) They have limited numbers of ribosomes so protein production is slow.
D) The mycolic acid in their cell walls requires signification metabolic investment.
E) They lack a cell wall and are extremely fragile.