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:Briefly, mice, after acclimation, were randomly assigned into 8 groups of 15 each, housed individually and fed the AIN93G diet, the high-fat diet, or the corresponding SPI-containing diets with or without access to in-cage activity wheels (Lafayette Instrument, Lafayette, IN, USA) [19].
Category: