单项选择题 In the event of a fire, the doors to a stair tower must be closed to prevent the spread of fire by （）.

单项选择题 When an oil fire has been extinguished, the surface of the oil should be kept covered with foam to prevent （）.

单项选择题 The process that occurs when heat is generated by a chemical reaction within a substance and continues to a point of ignition is known as （）.