Explanation
Correct answer: D.
Choice D is the best answer. The convention being tested here is pronoun-antecedent agreement. The singular pronoun "it" agrees in number with the singular antecedent "object."
Why the other choices are wrong
Choice A
Choice A is incorrect. The singular pronoun "this" is used to refer to a specific thing, but here there is no specific object being referred to. Instead, the sentence is referring back to a hypothetical object that Cave might use in a Soundsuit.
Choice B
Choice B is incorrect. The singular pronoun "that" is used to refer to a specific thing, but here there is no specific object being referred to. Instead, the sentence is referring back to a hypothetical object that Cave might use in a Soundsuit.
Choice C
Choice C is incorrect because the plural pronoun "these" doesn’t agree in number with the singular antecedent "object."