A Current Problem in Modern Medicine Is the Development of Drug

A current problem in modern medicine is the development of drug resistance mutations. This occurs when a mutation arises in a patient making him/her resistant to a drug and thus rendering the drug useless in treating a specific disease. Many useful drugs are competitive inhibitors of specific enzymes, and the drug-resistance mutations prevent the binding of the drug. These types of mutations, in addition to preventing competitive inhibitor binding, can also sometimes reduce the activity of the enzyme. Why is that the case?

A) These mutations most likely affect an allosteric site on the enzyme
B) These mutations lower the activation energy of the reaction catalyzed by the enzyme
C) Binding to the competitive inhibitor is essential for the function of the enzyme
D) These mutations most likely change the shape of the active site of the enzyme