The correct option is B Substrate site
When the linear chain of amino acids fold on themselves to form the tertiary structure, some amino acids come closer to each other and form the active site. The active site of an enzyme provides a uniquely structured platform for the reactant molecules to interact and form the product molecules. High specificity of the enzymes is because of the presence of active site. Active site is also known as substrate site (because the substrate fits here).
Allosteric site is any site other than the active site. It is different from the active site. binding of the substrate to this site will not result into a fruitful reaction. Inhibitors might bind to this site thus inhibiting the reaction.