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:Activating marks include the trimethylation of the fourth lysine on histone 3 (H3K4me3), which is associated with active promoters at genes enriched in CpG islands (see below), and acetylation of the 27th lysine of histone H3 (H3K27Ac), which is a mark of active enhancers, whereas repressed chromatin states are often marked by H3K27me3 [30].
Category: