Enzymes enhance the rate of reaction by 
(a) Forming a reactant-product complex
(b) Changing the equilibrium point of the reaction
(c) Combining with the product as soon as it is formed
(d) Lowering the activation energy of the reaction
(d) Enzymes enhance the rate of a reaction by just lowering the activation energy (the energy required for substances to react and get converted into product) of a reaction.