Study the following four statements: [P]: Gram negative bacteria produce potent pyrogenic substances called endotoxins [Q]: Ethylene oxide mixed with carbon dioxide or fluorinated hydrocarbons is used in gas sterilization [R]: D value is the time (for heat or chemical exposure) or the dose (for radiation exposure) required for the microbial population to decline by one logarithmic unit [S]: Spores of Geobacillus stearothermophilus (Bacillus stearothermophilus) are used for sterility testing of moist heat sterilization process Choose the correct answer.