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:biofuel production is in the form of ethanol derived from starch- or grain-based feedstocks, with over 90% of the biofuels produced and used domestically coming from corn (Groom et al., 2008).
Category: