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 cloning of hybridoma cells, culture supernatants were screened using indirect immunofluorescence microscopy (IIFM) with air-dried IF cells (Galfre & Milstein, 1981; Iwatani et al., 2005).
Category: