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:To get a rough approximation of the divergence time for the main phylogroups, we used both the higher and the lower sequence divergence rates proposed by Pinho et al. (2007) for the ND4–tRNALeu mitochondrial fragment (2.78% and 1.74% per million years, respectively).
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