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