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:A number of studies have delineated in DAFC-66D the 320bp Amplification Control Element on the third chromosome, ACE3, required for high levels of amplification (Figure 3C) (de Cicco and Spradling, 1984; Delidakis and Kafatos, 1989; Orr-Weaver et al., 1989; Orr-Weaver and Spradling, 1986).
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