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:In agreement with previously reported data (48, 53), RA treatment of the neuroblast-like (N-type) and RA-sensitive SY5Y and KCNR cell lines caused a marked morphological differe tiation characterized by the extension of neurites exceeding at least twice the length of the cell soma clearly detectable after 4 days (Fig.
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