The correct answer is A) flammability. The primary hazard of liquefied petroleum gas (LPG) and liquefied natural gas (LNG) is their high flammability. Both gases are highly combustible and can ignite easily, posing a significant fire and explosion risk. This is the key safety concern with the handling and transportation of these liquefied gases. The other answer choices are not the primary hazards. Temperature and pressure can be managed through proper storage and handling procedures, while toxicity is a secondary concern compared to the overriding flammability risk.