The correct answer is option 4, conduction. Veins seen in the leaves play a crucial role in conducting water, nutrients, and sugars throughout the plant. They act as a transportation system, similar to blood vessels in animals. The veins consist of xylem and phloem tissues. Xylem is responsible for conducting water and minerals from the roots to the leaves, while phloem transports sugars produced during photosynthesis from the leaves to other parts of the plant. This process of conduction helps in maintaining the plant`s overall growth and survival. Therefore, while options 1, 2, and 3 (photosynthesis, transpiration, and storage) are important processes in plants, veins primarily serve the function of conduction.