Answer
C.) slows down a reaction by increasing activation energy
Step-by-step explanation
Inhibitors are compounds that modify the catalytic properties of the enzyme and, therefore, slow down the reaction rate, or in some cases, even stop the catalysis. Such inhibitors work by blocking or distorting the active site.
Inhibitors, on the contrary, increase the energy of activation of the reaction.
The correct option is
C.) slows down a reaction by increasing activation energy