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:RNA interference in ticks Genes for RNAi were selected based on previous results in R. microplus or Dermacentor variabilis demonstrating the effect of gene knockdown on tick attachment, mortality, and/or fertility (de la Fuente et al. 2007b; 2008).
Category: