Hi jailena,
Here's the stimulus:
C = chordates
T = tracheophytes
P = member of Pteropsida
H = member of family Hominidae
Premise: C
T
Premise: P
T
(Inference: P
C)
Conclusion P
H
In order to draw a conclusion that P
H, we need to find something that puts H in a category that would rule out P. Our inference above that P
C means that if all H are C, P's cannot be H.
Answer choice (A) is something we can't draw that conclusion from because we end up with two premises that don't connect. We'd have P
T and H
T, but you cannot connect P and H in that scenario. Structurally, you can't connect the two sufficient conditions even if they have the same necessary condition.
All dogs are animals. D
A
All cats are animals. C
A
We can't connect dogs and cats there. We don't know if all dogs are cats, some dogs are cats, or no dogs are cats. There isn't a way to connect that chain. It's the same structural chain in answer choice (A).
Hope that helps!
