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:Cell cycle progression is driven by changes in cyclin–CDK complexes, and if control of the cell cycle is disrupted, progress through the cycle might be stimulated by overexpressed cyclins, enhanced CDK activity or inactivated CDK inhibitors (Malumbres and Barbacid, 2001; Chulu and Liu, 2009).
Category: