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.