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:Isolation of Full-Length ACIF1 Clones
The 131-bp cDNA-AFLP fragment for ACRE189 was used as probe to screen a cDNA library established from elicited tobacco cells (Durrant et al., 2000).
Category: