Most drugs that inhibit the synthesis of the cell wall act by
a. preventing the cross-linkage of nam subunits
b. blocking the secretion of cell wall molecules from the cytoplasm
c. preventing the formatioon of lactamases
d. preventing the formation of alanine-alanine bridges
e. disrupting the formation of the mycolic acid layer of the cell wall

a. preventing the cross-linkage of NAM subunits

Explanation:

The bacterial cell wall is made of peptidoglycan which is a polymer of alternating  N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) residues. The NAM residues  are crosslinked to impart additional strength to the cell wall.

Most of the antibiotics that target the cell wall synthesis in bacteria inhibit the enzyme of transpeptidation which in turn cross-links the NAM residues of the polysaccharide chains of the bacterial cell wall. Examples of these antibiotics include penicillins and cephalosporins.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.