Explanation
Correct answer: A.
Choice A is the best answer. “Later” logically signals that the letter-writing discussed in this sentence occurred later in a chronological sequence of events than did the antidiscrimination case discussed in the previous sentence.
Why the other choices are wrong
Choice B
Choice B is incorrect because “for instance” illogically signals that the letter-writing discussed in this sentence is an example of the antidiscrimination case discussed in the previous sentence. Instead, the letter-writing is an event that occurred after the court case.
Choice C
Choice C is incorrect because “in other words” illogically signals that the letter-writing discussed in this sentence is a paraphrase or restatement of the antidiscrimination case discussed in the previous sentence. Instead, the letter-writing is an event that occurred after the court case.
Choice D
Choice D is incorrect because “rather” illogically signals that the letter-writing discussed in this sentence is an alternative to the antidiscrimination case discussed in the previous sentence. Instead, the letter-writing is an event that occurred after the court case.