The correct option is A fleece of sheep
Wool is an animal fibre obtained from the fleece of animals like sheep, goats, camels, alpacas, llamas and yaks.
Silk is also an animal fibre. It is obtained from the cocoons of silkworms.
However, jute and cotton are plant fibres. Jute is obtained from the stem of the jute plant while cotton is obtained from the seeds of cotton plants.