The correct option is B Acrylic
Acrylic is a good alternative for wool. Most of the sweaters available in market are not made from natural wool, though they appear like wool. These are prepared from acrylic, a synthetic fibre having feel and texture like that of wool.
The clothes made of natural wool is quite expensive, whereas the clothes made from acrylic are relatively cheap.
Rayon, cotton and silk won't save us from the cold as clothes made from them are not warm.