What is a specific region of an enzyme where a substrate binds and the chemical reaction occurs

The correct answer is an active site.  

The active site, in biology, refers to the region of an enzyme where the molecules of substrate combine and goes through a chemical reaction. The active site comprises of the residues, which produce temporary bonds with the binding site (substrate) and residues that catalyze a reaction of that substrate, that is, the catalytic site.  

i think the answer is a.keratin is the pigment responsible for skin color.