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 cDNA produced was homopolymer dC-tailed and annealed into dG-tailed PstI-cut plasmid pAT153, and used to transform Escherichia coli strain HB101 (Maniatis et al., 1982).
Category: