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:Our reasons for choosing this VHC were (1) the valve design with baffling to improve drug delivery, (2) the visual indication of inspiration and face mask seal via the Flow-VU indicator, (3) the charge-dissipative polymer, and (4) the availability and design of various sizes of mask.
Category: