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:Nadolol, a nonselective Œ≤-blocker for the Œ≤1- and Œ≤2-AR, was selected because previous studies revealed this drug to be a full inverse agonist at the Œ≤2-AR (Bond et al. 1995; Wisler et al. 2007).
Category: