I think it is B.
A - out of scope
C - We donot know whether the compound is introduced in the brain to cure the disease.
D - Out of scope because of "variation of amount"
E - Out of scope.
Animals with a certain behavioral disorder have unusually high level of aluminum in their brain tissue. Since a silicon-based compound binds to aluminum and prevents it from affecting the brain tissue. Animals can be cured of the disorder by being treated with the compound.
The argument is based on which one of the following assumptions?
(A) Animals with the disorder have unusually high but invariable levels of aluminum in their brain tissue.
(B) Aluminum is the cause of the disorder rather than merely an effect of it.
(C) Introducing the compound into the brain tissue has no side effects.
(D) The amount of the compound needed to neutralize the aluminum in an animal's brain tissue varies depend-ing upon the species.
(E) Aluminum is never present in normal brain tissue.
Thnx & Rgds,