Explanation
Correct answer: D.
Choice D is the best answer. “However” logically signals that this sentence, which indicates that the Pūhāhonu volcano may be larger than the Mauna Loa volcano, offers a contrast to or refutation of the previous assumption that Mauna Loa is the largest shield volcano.
Why the other choices are wrong
Choice A
Choice A is incorrect because “secondly” illogically signals that this sentence merely offers an additional or secondary point concerning the previous assumption that Mauna Loa is the largest shield volcano. Instead, the sentence offers a contrast to or refutation of that assumption.
Choice B
Choice B is incorrect because “consequently” illogically signals that this sentence offers a result or consequence of the previous assumption that Mauna Loa is the largest shield volcano. Instead, the sentence offers a contrast to or refutation of that assumption.
Choice C
Choice C is incorrect because “moreover” illogically signals that this sentence merely adds to the previous assumption that Mauna Loa is the largest shield volcano. Instead, the sentence offers a contrast to or refutation of that assumption.