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:As such, the analysis of aDNA has been greatly enabled by NGS (Green et al. 2010; Krause et al. 2010; Rasmussen et al. 2010; Meyer et al. 2012).
Category: