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:Transient expression of SV40 small t activates MEK and MAP kinase in a PP2A-dependent fashion (51, 53), but the precise role of PP2A in the Ras/MAP kinase pathway is unresolved.
Category: