Volumetric composition of flue gas analysed with the Orsat apparatus is : CO2 = 12%, O2 = 8%, CO = nil, N2 = 80%. This flue gas composition indicates that_________________?

A. Pure oxygen has been used for combustion
B. Nitrogen percentage in the fuel is very high
C. Excess air has been used for combustion
D. Hydrogen is not present in the fuel