An LPG gas cylinder regularly used in the household contains a mixture of butane an propane. If 5 litres of this mixture on complete combustion produces 17 litres of CO2 at atmospheric pressure and 25°C, then the ratio of butane to propane in the mixture (Assume that both the gases in the cylinder are in vapour phase)
(A) 3 : 2
(B) 2 : 3
(C) 4 : 1
(D) 1 : 4