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.
davealtsNovember 10, 2019
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.
