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:Extracellular signal-regulated kinase 1 and 2 (ERK1/2), the c-Jun amino-terminal kinase (JNK 12/3), p38 kinase, and ERK5 are the four alternative MAPKs activated by distinct stimuli [1].
Category: