Read the sentence below:

“Scientists have succeeded in copying the silkproducing genes of the Golden Orb Weaver spider and are using them to create a synthetic material which they believe is the model for a new generation of advanced bio-materials.”

Source: IELTS: International English Language Test System. Specimen Materials 2003 (updated January 2005). British Council; IELTS
Australia; Univ. of Cambridge ESOL Examinations, p. 11.

In the sentence given, the underlined pronoun (they) refers to: