Explanation
Correct answer: B.
Choice B is the best answer. "Fittingly" logically signals that the information in this sentence—that the audience was amazed when Malinin landed the first quad axel—describes a suitable or appropriate reaction to the completion of this extremely difficult jump.
Why the other choices are wrong
Choice A
Choice A is incorrect. "Moreover" illogically signals that the information in this sentence merely adds to the previous information about the difficulty of completing a quad axel. Instead, the audience’s amazement is a suitable or appropriate reaction to this accomplishment.
Choice C
Choice C is incorrect. "Next" illogically signals that the information in this sentence is simply the next step in a process. Instead, the audience’s amazement is a suitable or appropriate reaction to the accomplishment.
Choice D
Choice D is incorrect. "However" illogically signals that the information in this sentence is in contrast or an exception to the difficulty of completing a quad axel. Instead, the audience’s amazement is a suitable or appropriate reaction to this accomplishment.