Correct Option: D

The veins are the vascular tissue of the leaf and are located in the spongy layer of the mesophyll. They are typical examples of pattern formation through ramification. The pattern of the veins is called venation. The veins are made up of: Xylem: tubes that bring water and minerals from the roots into the leaf; and Phloem: tubes that usually move sap, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf. Veins lend support to the leaf tissue, helping it keep its shape, like the ribs of an umbrella help it keep its umbrella shape. They conduct substances within the leaf, rather like the veins in our own bodies conduct blood. So their primary function is the conduction or transportation of nutrients.