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:The most common prebiotics used in humans are fructo-oligosaccharides (FOS) of different polymerization degrees (Guerreiro et al., 2016), either obtained from vegetables by hydrolysis or enzymatically synthesized (Flores-Maltos et al., 2014).
Category: