The saturation pressure \(P_{\text{sat}}\) of a pure liquid is represented by an equation of the form:
\[
\ln P_{\text{sat}} = A - \frac{B}{T},
\]
where \(A\) and \(B\) are constants, and \(T\) is the absolute temperature. For this substance, which of the following expression for the specific entropy difference between the saturated vapour and the saturated liquid phase \((s_{fg})\) is correct?