I believe the correct answer is the final option - He used a background of simple Classical columns and arches that don't detract from the figures.
If you take a look at the painting, you will see that you cannot learn much about history because you don't know what is going on, so A is incorrect. B is also incorrect because the colors don't detract from the story. C is incorrect because we don't know if that is true. D is the correct answer because you can see in the painting that the columns are in the background, just to provide a nice view.
