The correct answer is: C. Xylem
Root pressure is a positive pressure that develops in the xylem of roots. It is caused by the active transport of ions from the root cells into the xylem. This creates a concentration gradient, which causes water to move into the xylem by osmosis. Root pressure is a major force that drives the upward movement of water in plants.
The cortex is the layer of cells between the epidermis and the phloem. It is made up of parenchyma cells, which are cells that are involved in storage and transport. The phloem is the vascular tissue that transports sugars and other organic molecules from the leaves to other parts of the plant. The pith is the central core of the stem or root. It is made up of parenchyma cells, which are cells that are involved in storage and transport.
Root pressure is not developed in the cortex, phloem, or pith. It is developed in the xylem.