What is the function of the part labelled X in the figure given below?

• A.  It conducts food to the leaves and water to other parts of plants.
• B.         It conducts water to the leaves and releases oxygen and carbondioxide into the air.
• C.         It provides support to the leaf and help in transportation of water, minerals and food materials.
• D.         It throws out excess water in the form of water vapour into the air.