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:In this study, we used 2iL medium plus a PKC inhibitor, forskolin, and a TGF-b inhibitor for conversion and maintenance because some reports have suggested that a PKC inhibitor and forskolin facilitate conversion from the primed to the naive state (Hanna et al., 2010; Dutta et al., 2011; Takashima et al., 2014; Duggal et al., 2015; Qin et al., 2016).
Category: