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:PBN is widely used for ROS scavenging, and most importantly, has been shown to reverse the age-related oxidative changes and to reduce oxidative damage from ischemia/reperfusion injury.(40-44) The antioxidant activity of PBN protects biologically important molecules from oxidative damage.
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