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:For example, polymer based nanoparticles may be prepared by the well-known solvent evaporation method, in which the droplets of a nanoemulsion are composed of a volatile organic solvent in which the polymer is solubilized [28].
Category: