Predict the correct form of the Gibbs-Duhem equation in terms of the activity coefficient:

(a) \(x_{1} \frac{d \ln \gamma_{1}}{d x_{1}}=\left(1-x_{2}\right) \frac{d \ln \gamma_{2}}{d x_{2}}\)

(b) \(\left(1-x_{1}\right) \frac{d \ln \gamma_{1}}{d x_{1}}=x_{2} \frac{d \ln \gamma_{2}}{d x_{2}}\)

(c) \(x_{1} \frac{d \ln \gamma_{1}}{d x_{1}}=x_{2} \frac{d \ln \gamma_{2}}{d x_{2}}\)

(d) \(x_{1} \frac{d \ln \gamma_{1}}{d x_{1}}=\left(1+x_{2}\right) \frac{d \ln \gamma_{2}}{d x_{2}}\).