Correct answer: (a) Fibroin
Explanation
- A
Fibroin
Fibroin is the structural protein of natural silk from Bombyx mori (and other silkworms). It is not a laboratory polymer, so it is the non-synthetic substance and the official key.
- B
Lexan
Lexan is a brand of polycarbonate, a synthetic engineering plastic.
- C
Neoprene
Neoprene is polychloroprene, a synthetic rubber developed as an oil-resistant elastomer.
- D
Teflon
Teflon is polytetrafluoroethylene (PTFE), a fully synthetic fluoropolymer.
Summary. Official key is (a) fibroin. Silk fibroin is a natural protein fibre; Lexan, neoprene and Teflon are industrial synthetics. Do not treat ‘fibre’ as automatically synthetic. Honour the stored letter (a).
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