On May 13, 2003, a gas explosion accident occurred in Luling Coal Mine, Anhui Province, which sounded the alarm for the coal mining industry. However, in the next eight days, Liaoyang, Shanxi and Yunnan. (1) "5%-15%": this concentration range refers to the explosion limit of gas;

(2) Methane combustion can generate water and carbon dioxide, and the chemical equation of the reaction is CH4+2O2? Light it? . ? CO2+2H2O；

(3) The density of natural gas is less than that of air, and it will quickly rise to the upper part of the room after leakage, which is reasonable because the density of natural gas is less than that of air;

(4)A, check and close the air source valve to prevent further gas leakage, which can remove combustible materials and destroy combustion conditions, so A is correct;

B, window ventilation can dilute indoor combustible gas is not within the explosion limit range, so B is correct;

C, natural gas may explode when it meets an open flame, and turning on the electrical appliance will produce an electric spark and ignite the gas, so C is wrong;

So the answer is: (1) explosion limit; (2)CH4+2O2？ Light it? . ? CO2+2H2O； (3) Reasonable, because the density of natural gas is smaller than that of air; (4)AB。