The correct answer is A) preventing oxygen from reaching the burning material. The key to successfully fighting a Class B fire, which involves flammable liquids and gases, is to cut off the oxygen supply to the fire. This prevents the chemical reaction that sustains the fire from continuing. Cooling the material or making it fire-resistant (options C and B) are less effective for this type of fire, and absorbing heat (option D) does not directly address the oxygen supply. The reasoning behind this is based on the fire triangle, which outlines the three essential elements required to sustain a fire: fuel, heat, and oxygen. Cutting off the oxygen supply disrupts this triangle and extinguishes the fire.