The conclusion of the argument is: "we (those in physician's country) suffer significantly fewer ulcers, per capita, than they do."
Why? Despite the fact that those in the physician's country face the same dietary, bacterial, and stress-related causes of ulcers as the two other countries of roughly the same population size, prescriptions for ulcer medications in all socioeconomic strata in the physician's country are much rarer than in the other two countries.
What is the issue here? Just because there are less prescriptions for ulcer medications in all socioeconomic strata in the physician's country does not necessarily mean there are significantly fewer ulcers per capita. It could just be that there are fewer prescriptions given out in general. Maybe the people of the physician's country have home remedies for ulcers, or possibly prescriptions are not readily available to all those in the physician's country who suffer from ulcers.
Answer choice (D) states: "A person in the physician's country who is suffering from ulcers is just as likely to obtain a prescription for the ailment as is a person suffering from ulcers in one of the other two countries."
Answer choice (D) supports the argument. It helps show that those in the physician's country are not less likely than others to obtain a prescription. Thus, it quashes a potential challenge to the argument. If those in the physician's country are just as likely to obtain a prescription for ulcers as are those suffering from ulcers in one of the other two countries, then the evidence better supports the idea that those in the physician's country could actually be suffering less ulcers, per capita, than those in the other two countries.
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