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:For control purposes, the viruses RV-DUS2‚Äì11 (Falk et al., 2002) and RVHd65 (Besold et al., 2007) were employed.
Category: