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:Recent studies have shown that the global flux distribution in oleaginous Chlorella protothecoides and Chlamydomonas reinhardtii remains stable under nitrogen limiting conditions and is controlled by the availability of carbon precursors (Xiong et al. 2010; Fan et al. 2012).
Category: