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:…and Osmunda gametophytes and Glomus group A fungi, but it remains uncertain whether the gametophytes have specificity toward Glomus group A fungi as do mycoheterotrophic fern gametophytes (Winther and Friedman 2007, 2008, 2009), or specific Glomus A fungi are abundant in the sampling sites.
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