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:Thirdly, ErbB-3 is characterized by a defective mechanism of clearance from the cell surface (Baulida et al., 1996; Pinkas-Kramarski et al., 1996): instead of ligand-induced internalization and degradation in lysosomes, a mechanism shared by many growth factor receptors (Sorkin and Waters, 1993), ErbB-3 is destined primarily to enter the recycling pathway (Waterman et al.
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