AHSME 1967 Problem 4

Given $\frac{\log{a}}{p}=\frac{\log{b}}{q}=\frac{\log{c}}{r}=\log{x}$, all logarithms to the same base and $x \not= 1$. If $\frac{b^2}{ac}=x^y$, then $y$ is: $\text{(A)}\ \frac{q^2}{p+r} \text{(B)}\ \frac{p+r}{2q} \text{(C)}\ 2q-p-r \text{(D)}\ 2q-pr \text{(E)}\ q^2-pr$