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:Bifidobacteria is the third most common genus in the human intestine, constituting about 3% of the adult fecal flora and more than 75% of the infant fecal flora (Langendijk et al., 1995; Franks et al., 1998; Harmsen et al., 2000).
Category: