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:TfMA had lower sequence identity of 33~27% with α-amylase II from Thermoactinomyces vulgaris (Tonozuka et al. 1993), maltogenic amylase from Thermus sp.
Category: