To identify genes that put people at risk for depression,researchers have used

A) fMRI scans.
B) linkage analysis.
C) PET scans.
D) the DSM-5.

Linkage analysis is a technique used to identify genetic loci that are linked to a particular phenotype, such as susceptibility to depression. It involves identifying families where depression is more common than in the general population and looking for patterns of inheritance of genetic markers. Other options (fMRI, PET scans, DSM-5) may be useful in studying depression but are not specific to identifying genes associated with the disorder.