AHSME 1950 Problem 4

Reduced to lowest terms, $\frac{a^{2}-b^{2}}{ab} - \frac{ab-b^{2}}{ab-a^{2}}$ is equal to: $\textbf{(A)}\ \frac{a}{b} \textbf{(B)}\ \frac{a^{2}-2b^{2}}{ab} \textbf{(C)}\ a^{2} \textbf{(D)}\ a-2b \textbf{(E)}\ \text{None of these}$