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:…have developed a communication robot called Robovie that autonomously interacts with humans
by making gestures and utterances as a child’s freeplay (Kanda et al., 2004 a); however, Robovie is confronted with three major problems in elementary schools: 1) difficulties in sensing in the real world,…
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