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 instance, after only 1 week of storage the a-mannosidase activity showed a large decrease (,20% at 280uC and ,60% at 220uC), which confirmed the findings of a previous study (23).
Category: