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:The presence in Europe of two haplotypes (A and B) of the intron of the plastid gene for Leu tRNA (trnL) having different lengths (Spagnuolo et al. 2007) is interesting.
Category: