Disclosed is a system which enables the efficient utilization of urea for selective catalytic reduction of NOx by gasifying it and feeding it to a plurality of selective catalytic reduction units associated with a plurality of gas turbines. In the display device, a third electrode for promoting restoration of the droplet of a coloring liquid to a spherical shape is provided. One example method may include processing an interactive voice response customer call. Compared with the synthetic routes of ligands to be used in the activation of carbon-chlorine bonds in the prior arts, the preparation method of the present invention has the advantages of short route and easy operation.