Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The enzyme 3β-HSD has been localized in the ovary of a variety of mammalian species (Baillie et al., 1966; hamsters, Saidapur & Greenwald, 1978; humans, Sasano et al., 1990).
Category: