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:Transient expression of antibody fragments in tobacco leaves The system for transient expression in tobacco was based on MagnICON‚Ñ¢ vectors from Icon Genetics GmbH (Halle, Germany) [60,61].
Category: