A liquid/gaseous fuel containing hydrocarbons and high amount of sulphur is burnt with 40% excess air. The flue gas still contains large amount of carbon monoxide. This may be due to the

• A. presence of large quantity of hydrogen in the fuel.
• B. low calorific value of the fuel.
• C. high sulphur content in the fuel.
• D. lack of thorough mixing of fuel with air.