CR The brains of identical twins : GMAT Critical Reasoning (CR)
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# CR The brains of identical twins

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CR The brains of identical twins [#permalink]

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23 Mar 2008, 06:49
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Please don't forget explanations with the answers. Thanks

The brains of identical twins are genetically identical. 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. No such differences are found when neither twin is schizophrenic. Therefore, this discovery provides definitive evidence that schizophrenia is caused by damage to the physical structure of the brain.

23. Which one of the following is an assumption required by the argument?
(A) The brain of person suffering from schizophrenia is smaller than the brain of anyone not suffering from schizophrenia.
(B) The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment.
(C) The brain of a person with an identical twines is no smaller, on average, than the brain of person who is not a twin.
(D) When a pair of identical twins both suffer from schizophrenia, their brains are the same size.
(E) People who have an identical twin are no more likely to suffer from schizophrenia than those who do not.

24. If the statements on which the conclusion above is based are all true, each of the following could be true EXCEPT:
(A) People who lack a genetic susceptibility for the disease will not develop schizophrenia.
(B) Medications can control most of the symptoms of schizophrenia in most patients but will never be able to cure it.
(C) The brains of schizophrenics share many of the characteristics found in those of people without the disorder.
(D) It will eventually be possible to determine whether or not someone will develop schizophrenia on the basis of genetic information alone.
(E) Brain abnormalities associated with schizophrenia are the result of childhood viral infections that inhibit the development of brain cells.
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Re: CR The brains of identical twins [#permalink]

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23 Mar 2008, 07:51
The main sentence is emphasising that brain size of effected twin is smaller than other twin not suffering from the disease.

23.
(A) The brain of person suffering from schizophrenia is smaller than the brain of anyone not suffering from schizophrenia.
Use of "anyone" makes this extreme so this sentence should not be used.

(B) The relative smallness of certain parts of the brains of schizophrenics is not the result of schizophrenia or of medications used in its treatment.
Main sentence is concluding that the relative smallness of brain is because of disease. So this one is counteracting that so out.

(C) The brain of a person with an identical twines is no smaller, on average, than the brain of person who is not a twin.
Comparison between twin person and non-twin is not discussed, so out.

(D) When a pair of identical twins both suffer from schizophrenia, their brains are the same size.
Seems plausible. Keep it for backup.

(E) People who have an identical twin are no more likely to suffer from schizophrenia than those who do not.
Since sentence started with discussion on twins and concluded in general (for all with or without twins), so this is the assumption that best fits

Answer E.
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Re: CR The brains of identical twins [#permalink]

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23 Mar 2008, 07:52
23 B it protects cause-effect reasoning in the chain: damage of certain parts of the brains --causes-> schizophrenia

24 D the passage : [twins are genetically identical] --> [only one of a pair of identical twins is a schizophrenic] --> schizophrenia is not a genetic-determined disease.
D contradicts to the passage and cannot be true.
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Re: CR The brains of identical twins [#permalink]

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23 Mar 2008, 09:14
OA 23) B 24) D.

I still don't understand 23. Can someone pleas explain? Thanks
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Re: CR The brains of identical twins [#permalink]

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23 Mar 2008, 09:20
Vavali wrote:
I still don't understand 23. Can someone pleas explain? Thanks

......Therefore, this discovery provides definitive evidence that schizophrenia is caused by damage to the physical structure of the brain.

denial test:
(B*) The relative smallness of certain parts of the brains of schizophrenics is the result of schizophrenia or of medications used in its treatment.

Therefore, damage of the brain is an effect of schizophrenia or medications and is not a cause!
It destroys the conclusion.
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Re: CR The brains of identical twins [#permalink]

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23 Mar 2008, 11:16
thanks Walker
Re: CR The brains of identical twins   [#permalink] 23 Mar 2008, 11:16
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# CR The brains of identical twins

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