Silk, the natural form of fibre is obtained from

(a) Sheep

(b) Cocoon

(c) Jute plants

(d) Cotton balls

The correct answer is (b) Cocoon.

Silk is a natural animal fibre produced by the larva of the silk moth, commonly known as a silkworm. To protect itself during its pupal stage, the silkworm spins a protective casing around itself called a cocoon. This cocoon is made from a single, continuous thread of raw silk, which is harvested and processed to create silk fabric. 

The other options are sources for different types of fibres:

• (a) Sheep: Provide wool.
• (c) Jute plants: Provide jute fibre.
• (d) Cotton balls: Provide cotton fibre.