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:These PKC (1) isoforms can be divided into the following three subgroups based on cofactor requirements: conventional PKCs (a, b, and g), which are dependent on Ca(21) and diacylglycerol (DAG) for activity; novel PKCs (d, e, h, and u), which are not dependent on Ca(21) but are activated by DAG; and atypical PKCs (z, l, and i), which are not dependent on Ca(21) and are not stimulated by DAG (7).
Category: