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:In addition, evaluation of recombination by construction of incongruent phylogenetic trees (Fu et al., 2011) based on non-recombinant and recombinant region of the VP1 gene sequence was done using MEGA software version 5.0 (Tamura et al., 2011).
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