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:39
Characterization of Streptomyces antibiotic inhibition and resistance
Streptomyces antibiotic inhibition and resistance profiles were determined using
10 standard reference isolates described in Davelos et al. (2004b).
Category: