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:Very young (8-10 weeks old) rats were used in this study because it has been shown that younger rats are more sensitive to dietary salt loading than older ones (Dahl et al., 1968; Obiefuna et al., 1991; Sofola et al, 2002).
Category: