An interesting one -- the answer is A, without any doubt. In order to understand why, we have to start by understanding exactly how Roger is attacking Gloria. Without knowing that, we can't reliably determine how to refute the attack.
Gloria's argument is obviously an analogy: Her evidence is that there is nothing wrong with forcing people to pay taxes to support the local water supply, even if they choose not to buy "non-government" water instead of using the "government" supply. She concludes (by analogy) that there is nothing wrong with forcing people to pay taxes to support schools, even if they choose to buy "non-government" education instead of using the "government" schools.
Roger replies by saying that because people are forced to attend school of some type by law, those who choose not to use "government" schools must pay twice, and this is unfair. He claims that this makes Gloria's argument illogical. Because her argument was constructed by analogy, the only way to make it "illogical" would be to show that the analogy does not hold -- i.e., that the two things being compared are NOT alike in the ways that they should be alike if the argument is to work.
Therefore, when Roger claims that his statement makes Gloria's argument "illogical", he is actually claiming that the critical piece of evidence in his argument -- the fact that people are forced to attend school by law -- is NOT true for water. Choice A refutes this by pointing out that people ARE forced to drink water, although the compulsion comes from physical necessity, not from law.
Choice D is unrelated to the structure of Gloria's argument, and so it can neither refute nor support the charge of illogicality. In fact, both Roger and Gloria have accepted the truth of Choice D from the outset. Roger states it, and neither of Gloria's statements would make sense if she did not accept Choice D as true.
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