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:elegans, ebf mutant mice, chicks, Xenopus, and in cell lines, have revealed a number of neuronal genes that are regulated by EBF transcriptional activity [2,7,8,15-17,19,53-56].
Category: