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:Previous studies in our laboratory have established that P450 1A5 and 3A37, orthologs to human P450 1A2 and 3A4, respectively, are the most important P450 isoforms responsible for the bioactivation of AFB1 in turkey liver (Rawal et al., 2010b; Klein et al., 2000; Yip and Coulombe, 2006).
Category: