This is a Strengthen with Necessary Premise question. The stimulus presents an argument. The conclusion is: this discovery provides definitive evidence that schizophrenia is caused by damage to the physical structure of the brain.
The premises in support are: (1) the brains of identical twins are genetically identical, (2) when only one of a pair of identical twins is a schizophrenic, certain areas of the affected twin's brain are smaller than corresponding areas in the brain of the unaffected twin, and (3) no such differences are found when neither twin are schizophrenic.
The trouble with this argument is that it assumes that the correlation of two facts (damage to the physical structure of the brain, and the existence of schizophrenia) means that one thing (damage to the physical structure of the brain) *causes* the second (schizophrenia).
This assumption is described in answer choice (B). As explained in the in-app answers, if you negate this answer choice, the argument in the stimulus falls apart. On a Strengthen with Necessary Premise question, that's how you know which answer is correct.
Hope this helps! Please let us know if you have any additional questions.
Irene-VeraApril 19, 2019
Why is C wrong?
jamesteemartinApril 26, 2019
When someone asks to explain A through E can you actually explain through all of the answer choices. Many find it beneficial to see why answer choices are wrong, not just why the correct one is correct.
RaviApril 27, 2019
@jamesteemartin,
Happy to help. Let's go through each of the answer choices. Since this is a strengthen with a necessary premise question, we can use the negation test (that is, negate each answer choice) to see if the negation makes the argument fall apart. If the argument falls apart, then we know that the answer choice in question is a necessary premise. If the argument doesn't fall apart with the negation, then the answer choice isn't a necessary premise.
(A) says, "The brain of a person suffering from schizophrenia is smaller than the brain of anyone not suffering from schizophrenia."
(A)'s negation says, "The brain of a person suffering from schizophrenia is not smaller than the brain of anyone not suffering from schizophrenia."
This is not necessary for the argument. The schizophrenic's brain is less developed than his twin's brain, but this does not mean that it must be smaller than the brain of any healthy individual.
(B) says, "The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment."
(B)'s negation is, "The relative smallness of certain parts of the brains of schizophrenics is the result of schizophrenia or of medications used in its treatment."
(B)'s negation eliminates some very important alternative causes. If schizophrenia or the treatment medications resulted in the lack of brain development (which is the negation), then the argument falls apart. This means that (B) is a necessary premise for the argument.
(C) says, "The brain of a person with an identical twin is no smaller, on average, than the brain of a person who is not a twin."
(C)'s negation is, "The brain of a person with an identical twin is smaller, on average, than the brain of a person who is not a twin."
(C) is not necessary because it discusses people outside of the experiment (people who don't have twins). The comparison in the argument that's used to support the conclusion depends solely on the data on twins, so (C)'s information isn't necessary to the argument.
(D) says, "When a pair of identical twins both suffer from schizophrenia, their brains are the same size."
(D)'s negation is, "When a pair of identical twins both suffer from schizophrenia, their brains are not the same size."
(D)'s negation does not wreck the argument because it focuses on a different type of scenario from the experiment (involving one healthy twin and one schizophrenic twin) that is used to support the argument's conclusion. As a result, it's not a necessary premise.
(E) says, "People who have an identical twin are no more likely to suffer from schizophrenia than those who do not."
(E)'s negation is, "People who have an identical twin are more likely to suffer from schizophrenia than those who do not."
The likelihood of suffering from schizophrenia is irrelevant to schizophrenia's relationship to brain development and size, so (E) is unnecessary for the argument. Its negation doesn't wreck anything in the argument in the stimulus.
Does this make sense? Let us know if you have any more questions!
