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:Along these zones, actin filaments polymerize, providing the force needed for constriction that floppy ER tubules lack (Korobova et al., 2013, 2014; Hatch et al., 2014).
Category: