The optic nerves of identical twins

[ashishpanday]

The optic nerves of identical twins are genetically identical. When only one of a set of identical twins is visually impaired, certain areas of the affected twin’s optic nerve are atrophied whereas the corresponding areas of the other twin’s optic nerve is unaffected. No such differences are found when neither twin is visually impaired. Therefore, this discovery proves definitively that blindness is caused by damage to the structure of the optic nerve.

The argument above depends upon which one of the following?

a.The optic nerve of a blind person is smaller than that of anyone not suffering from visual impairment.

b.The relative size of the optic nerve of visually impaired individuals is not the result of corrective treatments or medications used to treat visual impairment.

b.The optic nerve of a person with an identical twin is no larger, on average, than the optic nerve of a person who is not an identical twin.

d.When a set of identical twins are both visually impaired, their optic nerves are in the same relative condition.

e.Individuals who have an identical twin are no more likely to suffer from visual impairment than are those who do not.


I am unable to understand how B can be answer

[jlucero]

As per the forum rules, we need a verifiable source for the problem before we can deal with this question. If the question is not from GMAT Prep we will need to delete the thread.