Explanation
Correct answer: B.
Choice B is the best answer. "However" logically signals that the information in this sentence—that nothing in Copeland’s career matches her accomplishment of being the first African American woman named principal dancer at the American Ballet Theatre—offers a contrast or exception to the previous information about Copeland’s accomplishments.
Why the other choices are wrong
Choice A
Choice A is incorrect because "thus" illogically signals that the information that follows is a result of the previous information about Copeland’s accomplishments. Instead, the statement that nothing in Copeland’s career matches this accomplishment offers a contrast or exception to that information.
Choice C
Choice C is incorrect because "for example" illogically signals that Copeland’s statement about her greatest accomplishment exemplifies the claim about her accomplishments in the previous sentence. Instead, it offers a contrast or exception to that information.
Choice D
Choice D is incorrect because "second of all" illogically signals that the information in this sentence is a second, separate claim from the previous sentence’s information about her accomplishments. Instead, the statement that nothing in Copeland’s career matches this accomplishment offers a contrast or exception to that information.