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:Rabbit models of cavitary TB in which sensitization promotes cavitation employ higher infectious doses (i.e. 103-104 CFU) that are delivered in a liquid vehicle to a small area of the lung by bronchoscope (Kübler et al., 2015; Nedeltchev et al., 2009).
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