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:PPR7, a Small PPR Protein in C. reinhardtii
PPR7 (Cre01.g048750) is one of the two unusually small PPRs in C. reinhardtii (Tourasse et al., 2013).
Category: