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:, 2012), sentence transformation (Vanderwende, 2008), machine comprehension (Du et al., 2017; Zhou et al., 2017b; Yuan et al., 2017; Subramanian et al., 2017), question answering (Qin, 2015; Tang et al.
Category: