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 oxygen isotope ratios of the particles studied by the PE team are very similar to those of the equilibrated LL chondrites (Nakamura et al. 2011; Yurimoto et al. 2011), which match the spectroscopic observations by the Hayabusa spacecraft (e.g., Fujiwara et al. 2006; Abe et al. 2006; Okada et…
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