Explanation
Correct answer: C.
Choice C is the best answer. "Of course" logically signals that the information in this sentence—that "the wavy staircase and ornate floral tilework" of the Modernista hospital couldn’t actually grow in a forest—acknowledges an obvious limitation of, or qualification to, the previous claim that Modernista architects championed nature in their designs.
Why the other choices are wrong
Choice A
Choice A is incorrect because "furthermore" illogically signals that the information in this sentence merely adds to the previous claim that Modernista architects championed nature in their designs. Instead, the sentence acknowledges an obvious limitation in how literally that natural influence was expressed in the hospital’s features.
Choice B
Choice B is incorrect because "similarly" illogically signals that the information in this sentence is similar to the previous claim that Modernista architects championed nature in their designs. Instead, the sentence acknowledges an obvious limitation in how literally that natural influence was expressed in the hospital’s features.
Choice D
Choice D is incorrect because "thus" illogically signals that the information in this sentence is a result of the previous claim that Modernista architects championed nature in their designs. Instead, the sentence acknowledges an obvious limitation in how literally that natural influence was expressed in the hospital’s features.