Many Insecticides Contain Compounds Which Inhibit the Enzyme Acetylcholine Esterase

Many insecticides contain compounds which inhibit the enzyme acetylcholine esterase which is essential for respiration and other vital functions in insects.These compounds exert their inhibitory effects by covalently bonding to active site amino acid side chains.What would be the most likely explanation for the inhibitory effects of these compounds?

A) Bonding of these compounds denatures the enzyme disrupting its secondary and tertiary structure.
B) Bonding changes the primary structure of the enzyme profoundly affecting the activity of the enzyme.
C) These compounds compete for the active site of the enzyme where they bind covalently and block the subsequent binding of substrate molecules.
D) Covalent bonding of these compounds changes the pI of the enzyme which causes it to become less soluble and precipitate.
E) Bonding of these compounds raises the activation energy of the reaction catalyzed by the enzyme.