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:…turkey P450 1A and 3A orthologs with respect to AFB1 metabolism in liver microsomal and heterologously-expressed systems, which are, in fact closer to humans than those from either mice and rats (Rawal et al., 2010b; Gallagher et al., 1994, 1996; Ueng et al., 1995, 1997; Yip and Coulombe, 2006).
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