Optimized designs of heat exchangers, and, in particular, heat exchangers and assemblies comprising multi-exchangers or combo coolers comprising different heat exchanger parts or elements, and fins or separators of different types andor characteristics on the different tube parts of the heat exchanger results, are disclosed. Each toy character has one or more one or more electronic signal receivers, and an electronic system. The wheel set includes front and rear wheels disposed respectively on the front and rear ends of the bicycle frame. The hydrogen reacts with a catalyst formed on an anode electrode at the hydrogen side of the channel to release hydrogen ions which are absorbed into the PEM. Further, the connector is grounded through the metal elastic piece and the metal casing so as to actuate the circuit of the memory card. The light-receiving element whose light-receiving surface is in substantially contact with the ridge portion detects as the ridge portion a bright portion where the scattered light emerging from the finger reaches at a high intensity.