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:…1990; Vorontsov and Blekhman 2001; Zhao
et al. 2002; Kuznetsov and Proshchalykin 2006;
Kovář 2007; Hoàng 2007; Kuznetsov and Proshcha-
lykin 2007; Poutsma et al. 2008; Tyumaseva and
Guskova 2008; USDA-ROBO 2008; Sato et al. 2008;
Krivets and Korovinskaya 2009; Tyumaseva and
Zhdanova 2009;…
Category: