Dr. furth wonders if a specific brain chemical can be suppressed if a patient is given a large dose of vitamin
e. this curiosity is the step in the scientific method.

I would say that the answer is that this is the second step in the scientific method. This is a controlled experiment in that the patient is given a large known dose of vitamin e and then monitored for brain chemicals. First I think that it would have to be known what brain chemicals are present and their amounts or concentrations  to be able to know if any of them are suppressed. This is like monitoring background water quality in natural streams and lakes at the site of a proposed mine before mining to see if there are any adverse changes.

Dang it i was gonna answer but yeah its c

Olfactory epithelium i believe