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:SVCT2 has been detected in mice skeletal muscle (Kuo et al. 2004) as well as in two murine muscle cell lines (Savini et al. 2005, Savini et al. 2007b).
Category: