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 concentrations of fluoxetine and propranolol were chosen in order to represent high environmental concentrations (based on surface water, wastewater effluent, and predicted environmental concentrations) up to those shown to result in effects on fish [26–29], or where the fish plasma model [30] would predict concentrations above human therapeutic levels (Cmax).
Category: