单选题 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.
Which one of the following is an assumption required by the argument?

A、 The brain of a 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 twin is no smaller, on average, than the brain of a person who is not a twin.
D、 When a pair of identical twins both suffer from schizophrenia, their brains are the same size.
E、 (E) People who have an identical twin are no more likely to suffer from schizophrenia than those who do not.

【正确答案】 B

【答案解析】[解析] 本题的证据是精神分裂患者的大脑中的某些区域比正常人的小，结论是精神分裂症是由大脑的物质结构受损引起。因此要使证据支持结论，只要说明精神分裂症患者大脑中的某些区域较小不是由除了精神分裂症以外的其他原因引起的就可以了。由以上分析可知(B)排除了他因，是本题的辩论所依赖的假设，为正确答案；(A)认为患精神分裂症者的大脑较小是由精神分裂症引起的，对本题的结论构成了反对；选项(C)、(D)和(E)既不能作为本题结论成立的前提，也不能从本题的论述中合理地推出。