The correct option is D Wood fibres
Cells of sclerenchyma are dead, thick walled due to the presence of lignin. The secondary wall is free from the primary wall. The sclerenchyma cells are classified into fibers and sclereids. These fibers are grouped into xylary fibers and extra-xylary fibers. Xylary fibers, also called wood fibers are parts of xylem and are the longest among xylem elements.