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:The combination of a red-edge, yellow, and two infrared bands of WV-2 provide additional valuable information for vegetation classification [16–18], which may be particularly useful when spectrally similar components like shrubs and trees need to be separated.
Category: