To obtain integrated form of Clausius-Clapeyron equation, ln (P_{2}/P_{1}) = (ΔH_{V}/R) (1/T_{1} - 1/T_{2}) from the exact Clapeyron equation, it is assumed that the

A. Volume of the liquid phase is negligible compared to that of vapour phase

B. Vapour phase behaves as an ideal gas

C. Heat of vaporisation is independent of temperature