A reverse auction platform for selecting a transaction service is provided. According to the invention, a row in which all the pixels display black is focused on in a plurality of pixels arranged in matrix, and sampling of data which is to be inputted to the pixels arranged in the row is not performed. The middle region is subjected to a crossed cut molding process to provide a helical type of fume path, suitable to enhance the efficiency of the assembly, owing to an increased thermal exchange between the fumes and heated air flows. The answer sheet has a plurality of test data fields, including answer fields in which a test-taker can input answers. Accordingly, in the display device including the light sources arranged advantageously with respect to the manufacturing cost, the lives of the light sources can be extended by reducing the power consumption. More particularly, the invention relates to copolymer macromolecules containing relatively hydrophobic indicator component monomers, and hydrophilic monomers, such that the macromolecule is capable of use in an aqueous environment.