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:…force for molecular ratchet motion does not seem to have been under strong evolutionary pressure, given that the replicase already possessed the molecular ratchet mechanism of movement which was driven by RNA synthesis itself (as in modern multi-subunit RNA polymerases (Abbondanzieri et al.
2005)).
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