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:Unlabeled DNA substrates containing consensus 12-RSS, 23-RSS, Hox11 or non-specific DNA sequences (DAR81/82) were prepared from oligonucleotides described previously [11,24].
Category: