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:It was apparent that the AlkOH group content was comparable with previous results obtained with the one-stage organosolv pretreatments of poplar performed at milder conditions (165 C, 40 min, 1.0% H2SO4), (Pan et al., 2006b).
Category: