Explanation
Correct answer: D.
Choice D is the best answer. “As a result” logically signals that the claim in this sentence—that spiders can cling to and climb almost any surface—is because of the previous information about the bonding properties of spiders’ spatulae.
Why the other choices are wrong
Choice A
Choice A is incorrect because “for instance” illogically signals that the claim in this sentence exemplifies the information in the previous sentences. Instead, the claim is because of the previous information about the bonding properties of spiders’ spatulae.
Choice B
Choice B is incorrect because “however” illogically signals that the claim in this sentence contrasts with the information in the previous sentences. Instead, the claim is because of the previous information about the bonding properties of spiders’ spatulae.
Choice C
Choice C is incorrect because “similarly” illogically signals that the claim in this sentence is similar to, but separate from, the information in the previous sentences. Instead, the claim is because of the previous information about the bonding properties of spiders’ spatulae.