The enthalpies of combustion of carbon and carbon monoxide are $-393.5$ and $-283 \; kJ\; mol^{-1}$ respectively. The enthalpy of formation of carbon monoxide per mole is
( A ) $6765\; kJ$
( B ) $110.5\; kJ$
( C ) $-110.5\; kJ$
( D ) $-6765\; kJ$