Choice A is the correct answer.

1. Find Roots: Solve $x^2 - 9 = 0 \Rightarrow x = \pm 3$.
2. Sketch: The parabola $y = x^2 - 9$ opens upward.
3. Test: We want where the graph is below the x-axis ($< 0$).
4. Result: This occurs between the roots: $-3 < x < 3$.

Choice B is incorrect because that describes $x^2 - 9 > 0$ (outside the roots). Choice C is incorrect. Choice D is incorrect.