A receiving unit receives a display panel that displays an image and a lamp that provides the display panel with a light. The assay includes a ligand analogue conjugate having a linkage site and a binding site, a ligand receptor, and a sample. A single mask is used to form a via in the first element to expose the first contact and the second contact. The seller determines whether to accept the offer, based on various factors such as the offer price and the availability of appropriate products to satisfy the conditions of the offer.