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:Until now, research has mainly focused on the biological activities of chemicals extracted from the seeds and roots of J. mandshurica (Lee et al., 2000; Li et al., 2003a, 2003b; Min et al., 2002; Kim et al., 1998; Sugie et al., 1998), with few reports on the bioactive chemicals from the leaves.
Category: