The correct option is A water gas
Secondary fuels are fuels that are derived from some primary fuel or fuels through chemical or physical processes. These are fuels that are not found as a natural resource. The energy for these secondary fuels comes initially from primary energy sources.Secondary fuels are often made to maximize the ability for combustion to get energy into an engine. This means that secondary fuels are often an intermediate form of energy between the primary energy and the energy services. This intermediate form is also known as an energy currency but energy currencies also include electricity which not a fuel (see electricity as an energy currency).An example of secondary fuel is water gas