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:Studies on HA have shown previously that HA have the ability to decrease respiratory stress, and reduce hyperactivity in eastern rainbowfish fingerlings exposed to low pH during 96 h exposures (Holland et al., 2014a).
Category: