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:Ghrelin is a 28-amino acid peptide, with a n-octanoylation indispensable for its biologic activity, originally isolated in the stomach as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R) [1,2].
Category: