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 concepts used are the flipped classroom approach (Mason, Shuman, & Cook, 2013; McLaughlin et al., 2014; Prober & Khan, 2013; Strayer, 2012; Tucker, 2012) and the inverted classroom (Gannod, Burge, & Helmick, 2008; Mason et al., 2013; Strayer,
2012).
Category: