Fibre-forming polymers: pick the set in which all listed polymers are suitable for making fibres.

Introduction / Context:
Fibre formation requires polymers with adequate molecular weight, chain regularity, and ability to be spun (melt, solution, wet, or dry) into filaments that can be drawn and crystallised or oriented.

Given Data / Assumptions:

• Cellulose derivatives (e.g., cellulose acetate, rayon family) are classic fibre polymers.
• Polyamides (nylons) are archetypal synthetic fibres.
• Polyurethanes include elastomeric fibre types (e.g., spandex).

Concept / Approach:
Among the sets, only one contains three polymer families widely used for fibres. Butadiene rubbers and urea–aldehyde resins are not typical fibre materials. Polyisoprene is a rubber; while polyethylene can form fibres, its grouping with polyisoprene makes the set invalid. Silicon is not a thermoplastic polymer; PVC can be solution-spun in niche cases, but the set with silicon fails entirely.

Step-by-Step Solution:
Screen each set for any member that is not fibre-forming.Reject sets containing rubbers or thermoset resins when asked for fibre use.Select the set comprising cellulose derivatives, polyamides, and polyurethane.

Verification / Alternative check:
Commercial fibres: cellulose acetate, nylon-6/66, and spandex (PU) are well-established.

Why Other Options Are Wrong:
(a) Urea–aldehyde is a thermoset; butadiene copolymers are rubbers.(b) Polyisoprene is rubber; set invalid.(d) Silicon is not a fibre-forming thermoplastic polymer; set invalid.

Common Pitfalls:
Assuming any high-molecular-weight material can be spun; overlooking the need for drawability and structural orientation.

Final Answer:
Cellulose derivatives, Polyamides, Polyurethane