A system of controlling combustion of fuel in a boiler having an adjustable air-to-fuel ratio. A control circuit controls, during a test-mode operation, the memory cell so that a plate-line signal sent through the plate line to the memory cell and a bit-line signal sent through the bit line to the memory cell are set at a same potential. The phenol resin pulley for motor vehicles is almost free from swelling or shell cracking on the surface at a high temperature of 250 C. The method also includes coupling the first side portion to an object to enable the instructions to be covered by the first layer until removal thereof.