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:The MEK inhibitor PD98059, prevented AR induced by LPC (de Lamirande and Gagnon, 2002) but not by A23187 and zona pellucida (du Plessis et al., 2002).
Category: