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 PCR reactions were multiplex PCR using three sets of primers: Mycgen-F, Mycgen-R, Mycav-R; RD4F, RD4R, RD4intF; and RD10F, RD10R, RD10intR [28].
Category: