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:As indicated by our results and those of others (Rogers et al., 2010; Thill et al., 2006; Zeyons et al., 2009), the direct contact of the ceria nanoparticles with the cell wall/membranes is essential for cytotoxicity to occur.
Category: