The correct answer is C. synthesis gas.
Synthesis gas is a mixture of carbon monoxide and hydrogen. It is a starting material for manufacturing a number of organic compounds, including methanol, ammonia, and synthetic fuels.
Producer gas is a mixture of carbon monoxide, hydrogen, and nitrogen. It is produced by the incomplete combustion of coal or other carbonaceous materials. It is used as a fuel for industrial furnaces and boilers.
Natural gas is a mixture of methane, ethane, propane, butane, and other hydrocarbons. It is found in underground deposits and is a major source of energy.
Oil gas is a mixture of hydrocarbons that is produced from petroleum. It is used as a fuel for vehicles and other engines.
In conclusion, the correct answer is C. synthesis gas.