The correct answer is D. Lateral meristem.
Lateral meristem is a type of meristem that is responsible for the increase in girth of a plant. It is found in the vascular cambium and cork cambium. The vascular cambium produces new xylem and phloem cells, while the cork cambium produces new cork cells. These cells add to the thickness of the stem and root.
Tracheids are elongated, dead cells that are found in the xylem. They transport water and minerals from the roots to the leaves. Pericycle is a layer of cells that surrounds the vascular cambium. It can give rise to secondary roots and lateral meristem. Intercalary meristem is a type of meristem that is found in the internodes of some plants. It is responsible for the growth of the internodes.
Here is a diagram of a plant stem that shows the location of the lateral meristem:
The lateral meristem is located between the xylem and phloem. It is a thin layer of cells that is responsible for the increase in girth of the stem.