The conclusion here is "animals can be cured of the disorder by being treated with the compound."
The support provided? "Animals with a certain behavioral disorder have unusually high levels of aluminum in their brain" and "a silicon-based compound binds to aluminum and prevents it from affecting the brain tissue."
The author is clearly assuming that aluminum is the cause of the behavioral disorder because his support for treating the disorder using a silicon-based compound is that this compound binds to aluminum and prevents it from affecting the brain tissue.
This is a Strengthen with Necessary question, so we are looking for the necessary assumption.
(B) states "Aluminum is the cause of the disorder rather than merely an effect of it."
This clearly strengthens the argument because if aluminum is the cause of the disorder, the silicon-based compound that prevents aluminum from affecting the brain tissue would cure the disorder (i.e. by eliminating the cause).
Now let's negate (B) to make sure it is necessary. The negation of (B) is, "Aluminum is NOT the cause of the disorder rather than merely an effect of it."
Notice that (B) negated destroys the argument because if aluminum is not the cause of the disorder it would not be possible to treat the disorder with a silicon-compound that prevents aluminum from affecting the brain tissue.
Hope this helps! Please let us know if you have any other questions.
