Question

__is a natural fibre, with continuous filaments which can stretch upto 1km.

Answer 1

Hint: Fibre is a material that is much longer than it is wide, whether it be natural or man-made. Fibers are frequently used to create other materials. Fibers, such as carbon fibre and ultra-high-molecular-weight polyethylene, are frequently used in the strongest engineering materials.

Complete answer: Natural fibres, which include those generated by plants, animals, and geological processes, form or appear in the fibre form. Animal fibres are mostly made up of certain proteins. Silkworm silk, spider silk, sinew, catgut, wool, sea silk, and hair are examples.
Biological fibres, also known as fibrous proteins or protein filaments, are made up mostly of medically relevant and physiologically highly significant proteins, in which mutations or other genetic flaws can cause serious disorders. Collagen, tendons, muscle proteins like actin, cell proteins like microtubules, and many other proteins, such as spider silk, sinew, and hair, are examples.
Silk is a natural protein fabric that may be woven into textiles in various forms. Silk is a protein fibre made primarily of fibroin, which is generated by some insect larvae to build cocoons. The most well-known silk comes from the cocoons of mulberry silkworm Bombyx mori larvae raised in captivity (sericulture). Silk's gleaming look is due to the triangular prism-like structure of the silk fibre, which allows silk material to refract incoming light at different angles, resulting in various hues.
Silk is a natural protein fabric that may be woven into textiles in various forms.
Silk is made up primarily of the protein fibroin, which is synthesised by some insect larvae in order to construct cocoons.
Fibrils and filaments can reach up to one kilometre in length.
As a result, option A is the proper choice.

Note:
Silk manufacture began in China during the Neolithic period, but it later spread to other parts of the globe (Yangshao culture, 4th millennium BC). Silk manufacture was limited to China until the Silk Road was established somewhere in the second millennium BC, though China retained a virtual monopoly on silk production for another thousand years.