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:During the uplift of the Tibetan Plateau, river captures and flow reversals caused regional extension of the Yangtze River basin to the eastern Tibetan Plateau (Clark et al. 2004; Fan et al. 2005).
Category: