The correct answer is C) at the seat of the fire, starting at the near edge. When fighting a class "B" fire (a fire involving flammable liquids or gases) with a portable dry chemical extinguisher, the discharge should be directed at the seat of the fire, starting at the near edge. This is because the dry chemical agent works by interrupting the chemical reaction that sustains the fire, and directing the discharge at the base of the flames is the most effective way to smother the fire at its source. The other options are incorrect because directing the discharge over the top of the fire (A) or at the main body of the flames (D) would be less effective at reaching the seat of the fire, while banking the discharge off a bulkhead (B) could disperse the agent away from the fire's source.