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:The upregulated PDHC expression level upon ND was in line with the previous findings that upregulation of PDHCmediated acetylCoA synthesis contributed to the augmented TAG accumulation (Li et al. 2014b; Jia et al. 2015).
Category: