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 rationale for using hRPE cells was based on their ability to secrete L-dopa from tyrosine, catalyzed by the enzyme tyrosinase, as part of their eumelanin synthesis pathway (Ito and Wakamatsu 2008).
Category: