AMC 12 2000 Problem 11

Two non-zero real numbers, $a$ and $b,$ satisfy $ab = a - b$. Which of the following is a possible value of $\frac {a}{b} + \frac {b}{a} - ab$?

\textbf{(A)} \ - 2 \textbf{(B)} \ \frac {- 1}{2} \textbf{(C)} \ \frac {1}{3} \textbf{(D)} \ \frac {1}{2} \textbf{(E)} \ 2