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:…(Lee and Chun 1998; Lee et al. 2001; Söderman et al. 1994, 1996, 1999; Hjellstrom et al. 2003) and Hahb-4 from sunflower (Gago et al. 2002; Manavella et al. 2006), of which the expression is inducible by drought as well as by abscisic acid (ABA), which plays a central role in regulating…
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