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:We have used the sheep ovary model, since this is the most widely used animal model of whole ovary cryopreservation and is of comparable size to the human ovary (Bedaiwy et al., 2003; Revel et al., 2004; Arav et al., 2005; Courbiere et al., 2005, 2006, 2008; Imhof et al., 2006; Baudot et al., 2007; Bedaiwy and Falcone, 2007; Onions et al., 2008).
Category: