Explanation
Correct answer: B.
Choice B is the best answer. "In fact" logically signals that the critics’ claim at the end of this sentence—that the two editions are essentially two different novels altogether—offers additional emphasis in support of the previous claim that the differences between the editions are extreme.
Why the other choices are wrong
Choice A
Choice A is incorrect because "by contrast" illogically signals that the claim at the end of this sentence contrasts with the previous claim about the differences between the editions. Instead, the critics’ opinion offers additional emphasis in support of that claim.
Choice C
Choice C is incorrect because "nevertheless" illogically signals that the claim at the end of this sentence is true despite the previous claim about the differences between the two editions. Instead, the critics’ opinion offers additional emphasis in support of that claim.
Choice D
Choice D is incorrect because "in other words" illogically signals that the claim at the end of this sentence is merely paraphrasing the previous claim about the differences between the two editions. The critics’ opinion adds new information to the previous claim rather than simply paraphrasing it.