Which of the following findings led to the conclusion that schizophrenia may be caused by dopamine activity?
a) drugs that relieve schizophrenic symptoms have side effects similar to parkinson's disease.
b) parkinson's disease is known to be caused by excess levels of dopamine.
c) people with parkinson's disease are more likely to develop schizophrenia.
d) all of the above are correct findings.

Investigator a has biological specimens that are coded and linked to identifiers of the source individuals. investigator a provides the specimens to investigator b but does not provide the individual identifiers. investigator b agrees not to re-identify the source individuals. is investigator b's research using the biospecimens human subjects research according to the definition of human subjects research in the federal regulations?