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:Unlike the packed ER cisternae characteristic of professional secretory cells (Harding et al., 2001; Lee et al., 2005), the ER of adipocytes (d5) have few loosely dispersed cisternae with discernible ribosomes (Figure 3G) as shown previously (Novikoff et al., 1980).
Category: