The correct answer is B) The cargo tanks are used for one type of cargo only. The reason this is the correct answer is that LPG (liquefied petroleum gas) cargo tanks are typically dedicated to carrying a single type of LPG cargo, such as propane or butane. Since the tanks are not used for multiple cargoes, there is no need to perform gas-freeing (the process of removing flammable or toxic vapors from a cargo tank) between cargo loadings. The tanks can be refilled with the same type of LPG without requiring gas-freeing, as there is no risk of cross-contamination between different cargoes. The other answer choices are incorrect because: A) Cargo tanks are inspected less frequently than on oil tankers, but this does not directly relate to the need for gas-freeing; C) LPG is not compatible with all cargoes, so gas-freeing would be required if the tanks were used for different cargo types; and D) the high oxygen content of LPG does not make it nonvolatile, as it is still a flammable gas.