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 reovirus 1/L-induced ARDS, at day 9 postinoculation, there is a severe pneumonia (peribronchiolar lesions with lymphocytic infiltration) with the presence of hyaline membranes, which are pathognomonic for human ARDS (20, 21).
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