Answer: a. molecular recognition based on structural complementarity
Explanation: Enzyme specificity is the ability of an enzyme to bind/react with a particular substrate and/or catalyze a specific set of chemical reactions. It is the ability the an enzyme to choose, bind with the correct and exact substrate from a group of similar chemical reactions.
This enzyme specificity operates through the structural and conformational complementarity between an enzyme and a substrate and it is based on a molecular recognition pattern. This was introduced by Emil Fischer (Nobel prize winner) who proposed the “lock and key” model. He used this model to explain the high specificity of an enzyme for its substrate.