Explanation

Thank you for your question. The author of the stimulus has just negated a transitive conclusion. This is flawed reasoning. Let's look at each part of the stimulus first. P: TT or TG ==> SDP [when people experience throbbing in their teeth or gums, they have serious dental problems] P: SDP ==> TD or GD [if a dental problem is serious, it will be either tooth decay or gum disease] P: (not) TT and (not) TG [Sabina is not experiencing throbbing in her teeth or gums] C: (not) TD and (not) GD [so Sabina is neither suffering from tooth decay nor gum disease] That conclusion does not follow. You can't just negate both sides. Remember, don't just negate! The correct transitive is: TT or TG ==> SDP ==> TD or GD Now, let's look at the correct answer, answer choice (D). P: IP or IC ==> WCM [if interested in physics or chemistry, wise to consider career in medicine] P: (not) IP and (not) IC [Yolanda is not interested in physics or chemistry] C: (not) WCM [so it would not be wise for Yolanda to consider a career in medicine] Again: the same mistake. They've just negated both sides. Answer choice (A) uses prescriptive language (should) rather than descriptive language (as did the stimulus). Answer choice (B) is not flawed. P: LPS ==> MD and PT [a legally practicing psychiatrist must have both a medical degree and psychiatric training] P: (not) PT [Emmett has not undergone psychiatric training] C: (not) LPS [Emmett is not a legally practicing psychiatrist] That's actually a valid conclusion. The contrapositive of the first premise is: (not) MD or (not) PT ==> (not) LPS. The second premise (that Emmett has not undergone psychiatric training) triggers the conclusion (via the contrapositive) that Emmett is not a legally practicing psychiatrist. Answer choice (C) P: SNC ==> SI or A [if severe nasal congestion, then either sinus infection or allergy] Contrapositive: (not) SI and (not) A ==> (not) SNC [if neither sinus infection nor allergy, then not severe nasal congestion] Conclusion: (not) SI ==> (probably) (not) SNC This conclusion does not follow, but it's not the same flaw as in the stimulus. Answer choice (E) P: (not) Oph and (not) Opt ==> (not) STDED [if not an ophthalmologist and not an optometrist, then no specialized training in diagnosing eye defects] P: AD [Kim accurately diagnosed John's eye defect] C: Oph or Opt [Kim must be an ophthalmologist or optometrist] This conclusion also does not follow, but again, it's not the same flaw as in the stimulus. Hope this helps. Please let us know if you have any additional questions.

I summed the stimulus up as having two sufficient for a necessary. You could also have a unknown sufficient for the necessary so you cannot conclude that because there is an absence of the two sufficient that you don't have the necessary. This is why D jumped off the page. Having an interest in the two (chemistry, Physics) is sufficient for career in medicine, other interests like an interest in biology could also be sufficient for a career in medicine. This uses the same flaw in logic as the stimulus. I was able to come to this answer without diagramming just by understanding the flaw in the stimulus.