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:It was reported that ESCs may be short or long term cultivated on synthetic substrates in com mercial chemically defined media (Brafman et al., 2010; Mahlstedt et al., 2010; Higuchi et al., 2011; Lee et al., 2011; Nandivada et al., 2011; Valamehr et al., 2011; Ueda et al., 2012).
Category: