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:A recent in vitro study with MBD1-6 reported that MBD1-3 was compacted without Cu and adopted an extended conformation after Cu loading (Yu et al. 2017b), indicating a possible impact of Cu binding on the structural arrangements of both linkers and MBDs.
Category: