Explanation
Correct answer: B.
Choice B is the best answer. "On the contrary" logically signals that the information in this sentence—that Dies Irae’s appearance of depth is merely an illusion—contrasts with the previous statement about a viewer’s possible assumption regarding the street painting.
Why the other choices are wrong
Choice A
Choice A is incorrect because "additionally" illogically signals that this sentence is simply additional information about a viewer’s possible assumption regarding the street painting. Instead, the information about how Wenner achieved the illusion of depth contrasts with the previous sentence’s description of the illusion.
Choice C
Choice C is incorrect because "as a result" illogically signals that the information in this sentence is a result of, or caused by, a viewer’s possible assumption regarding the street painting. Instead, the information about how Wenner achieved the illusion of depth contrasts with the previous sentence’s description of the illusion.
Choice D
Choice D is incorrect because "next" illogically signals that the information in this sentence is the next step in a process. Instead, the information about how Wenner achieved the illusion of depth contrasts with the previous sentence’s description of the illusion.