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:Specifically, metagenomic DNA was amplified using the 16S V1 (27F) forward [14] and V3 (534R) reverse [15], and the 16S V3 (341F) forward and V4 (805R) reverse [39] primer pairs with added Illumina adapter overhang nucleotide sequences (Table 1).
Category: