Gram negative organisms are largely insensitive to benzyl penicillin because (a) They produce large quantities of penicillinase (b) They do not utilize D-alanine whose incorporation in the cell wall is inhibited by benzyl penicillin (c) Benzyl penicillin is not able to penetrate deeper into the lipoprotein-peptidoglycan multiplayer cell wall of gram-negative bacteria (d) Both (a) and (b)