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:, light and openness) are sufficient to make it aversive (Calatayud & Belzung, 2001; Russell, 1979); (c) the OF is, nevertheless, a relatively novel environment after four 2-min exposures, compared with the animal’s home cage; and (d) the aim of this selection experiment was to create two lines of mice, the divergence in emotionality being based on the more stable and enduring features of these animals, rather than only on an initial response to novelty (see Belzung & Griebel, 2001; Lister, 1990).
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