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:…allowed to walk freely for 1 h as a group inside a Petri dish (100 x 15 mm) lined with filter paper (Whatman Qualitative no. 5, particle retention > 2.5 μm) moistened with 1.0 ml of a suspension containing 2 x 10 8 conidia/ml (high dose) or 6 x 10 6 conidia/ml (low dose) (Rosengaus et al. 1998).
Category: