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:The age of giant nupDNA fragment A was calculated by dividing the corrected K value of type 2 substitutions (see Results) by the absolute substitution rate of the synonymous sites in the nuclear genes of rice (Ramakrishna et al., 2002).
Category: