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:Thus we selected BG01 and HUES-7, which were independentlyderived at BresaGen (Mitalipova et al., 2003) and Harvard University (Cowan et al., 2004) using different embryo culture, inner cell mass isolation, hESC culture and hESC passaging methods.
Category: