The correct option is
A Jute
Jute fiber is a phloem fiber, which is extra-xylary unbranched fiber with tapering ends, thick walls, narrow lumen. It is the longest fiber and is obtained from Corchorus.
Coir is obtained from the husk of coconut and is used in cottage industry to make products, as floor mats, doormats, brushes, mattresses, etc. Sunn hemp (Crotalaria juncea) is a legume, which yields soft, lignified fibers from its stem, which is utilized in the manufacturing of pulp and paper.
Cotton is the surface fiber of Gossypium. It is extracted from mature capsule of cotton plant.
So, the correct answer is option A.