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:As stated by Spyropoulos (2000), a hospital infrastructure is composed of:
(a) Human resources: physicians, nurses, administrative personal, technicians for equipment maintenance, etc. (b) Intensive therapy units, with an expensive infrastructure.
ll rights reserved.
ta Filho).
Category: