OG详解-OG5 文法 Q11

Choice D is the best answer. “Hence” logically signals that the information in this sentence about turtle shells—that people incorrectly assume they are exoskeletons—is a consequence of the shells appearing external to the animal.
Choice A is incorrect because “that being said” illogically signals that this sentence qualifies or contrasts with the previous information about turtle shells appearing external to the animal. Instead, it presents a consequence of that information. Choice B is incorrect because “however” illogically signals that this sentence contrasts with the previous information about turtle shells appearing external to the animal. Instead, it presents a consequence of that information. Choice C is incorrect because “for instance” illogically signals that this sentence provides an example supporting the previous information about turtle shells appearing external to the animal. Instead, it presents a consequence of that information.