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:Four viral proteins are able to bind nonspecifically to RNA (VP2, VP3, NSP2 and NSP5) [3, 24, 33] and three bind specifically to rotavirus mRNA sequences (VP1, NSP1 and NSP3) [4, 15, 23, 27].
Category: