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:If NusA is not present, antitermination still occurs, but in this case there is evidence that antipausing is the mechanism: Restricting elongation rate at the critical release site of an intrinsic terminator by reducing the substrate NTP concentration impairs antitermination in the absence of NusA, but not in its presence (126).
Category: