And so once again, as in step D, in step d for a sandwich allies that we wash our mixture to basically remove anything that is not bound. And because this is bound, this is not removed. And when we add our substrate into the mixture, because the enzyme will be present inside our solution, that enzyme will begin to readily convert that substrate into that product. And when this transformation takes place, that once again causes a color change. So we see the principle that we use is this color change reaction. It's the color change reaction that signifies the presence of either that antibody or that antigen in our sample.