During prenatal development, the time when a particular organ or body part is most vulnerable is the
a. critical period
b. last month of pregnancy
c. period of vulnerability
d. accommodation period

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?