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:1kb /3-actin cDNA (11) was released by BamHl digestion; the 662-base pair full length IGF-1 cDNA was obtained from plasmid phIGF-1 (12) by Pstl digestion; the Xbal-BamH\ fragment of the human IGF1-R cDNA was released from plasmid pCVN-IGF-lR
Category: