The correct answer is: A reflection over the x-axis
The transformation that would accomplish the change from Figure C to Figure D is a reflection over the x-axis.
This is because a reflection over the x-axis would result in the image being flipped vertically, which matches the transformation from Figure C to Figure D.
This is consistent with the properties of reflections, where the x-coordinates of the reflected image are the same as the original, and the y-coordinates are the opposite.
Therefore, the correct answer is: A reflection over the x-axis.