Explanation
Correct answer: A.
Choice A is the best answer. The convention being tested is the use of punctuation within a sentence. The dashes after "models" and "decision-makers" correctly separate the supplementary element "which assume that people are consistently rational decision-makers" from the rest of the sentence. This punctuation indicates that this element could be removed without affecting the grammatical coherence of the sentence.
Why the other choices are wrong
Choice B
Choice B is incorrect because a comma can’t be paired with a dash in this way to separate the supplementary element from the rest of the sentence.
Choice C
Choice C is incorrect because it fails to use appropriate punctuation to separate the supplementary element from the rest of the sentence.
Choice D
Choice D is incorrect because it interrupts the sentence at an illogical and grammatically incoherent point. The dash should be placed before "which," not after it, to mark the beginning of the supplementary element.