2007 Fermat Problem 20

The graph of the function y = ax^2 + bx + c is shown in the diagram. Which of the following must be positive?

\textbf{(A)} a \textbf{(B)} bc \textbf{(C)}\ ab^2\quad \textbf{(D)} b - c \textbf{(E)} c - a

If there are no answer choices shown, enter a numerical answer.

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