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:Probes EUB338 I-III (Amann et al., 1990; Daims et al., 1999) for the domain Bacteria and Gam42a with competitor (Manz et al.
Category: